The 2020 presidential race is starting to heat up, and the Democratic field could get crowded — fast.
Elizabeth Warren, Julian Castro, Bernie Sanders and a handful of other well-known Democrats and progressives have tossed their hats into the presidential ring, and more popular politicians are likely to follow suit in the coming weeks.
Former Vice President Joe Biden — as predicted — has stayed silent about his plans thus far.
Apparently, Biden's advisers have floated Rep. Beto O’Rourke, D-Texas, as a potential running mate, given his recent rise in popularity. Despite losing the Texas Senate race to Republican Sen. Ted Cruz, O'Rourke is still considered a "rising star" in his party.
In a January op-ed in The New York Times, titled "Run, Joe, Run," a columnist advised Biden to enter the race because he has "strengths that no other Democratic candidate does," citing his decades of experience and ties to the Obama administration.
“If it turns out that I am the best candidate to beat Donald Trump, then I will probably run.”
As some political heavyweights continue to mull it over, take a look at those who have already made moves ahead of the 2020 election.
Sen. Bernie Sanders, I-Vt., is hoping to make a comeback after aiming to inspire a progressive movement during his 2016 campaign.
“If there’s somebody else who appears who can, for whatever reason, do a better job than me, I’ll work my a-- off to elect him or her,” Sanders told New York Magazine in November. “If it turns out that I am the best candidate to beat Donald Trump, then I will probably run.”
During an interview on Vermont Public Radio on Feb. 19, Sanders confirmed he's running again.
“We began the political revolution in the 2016 campaign, and now it's time to move that revolution forward,” he told the radio station.
Sen. Amy Klobuchar, D-Minn., announced her decision to join the 2020 presidential race on a snowy Feb. 10 in Minneapolis.
"For every American, I'm running for you," Klobuchar, who has served in the Senate since 2007, told a crowd. "And I promise you this: As your president, I will look you in the eye. I will tell you what I think. I will focus on getting things done. That's what I've done my whole life. And no matter what, I'll lead from the heart," the three-term senator said.
Klobuchar, 58, is known as a straight-shooting, pragmatist willing to work with Republicans, making her one of the Senate's most productive members at passing legislation.
Sen. Cory Booker, D-N.J., jumped into the 2020 race on Feb. 1, vowing to unite what he considers a currently divided nation.
"I believe that we can build a country where no one is forgotten, no one is left behind; where parents can put food on the table; where there are good-paying jobs with good benefits in every neighborhood; where our criminal justice system keeps us safe, instead of shuffling more children into cages and coffins; where we see the faces of our leaders on television and feel pride, not shame," Booker said in a campaign video, subtly jabbing at President Donald Trump.
"It is not a matter of can we, it's a matter of do we have the collective will, the American will?" he added. "I believe we do."
Booker, a former mayor of Newark, New Jersey's largest city, won a special Senate election in 2013 to replace Democrat Frank Lautenberg and then won a full Senate term in 2014. He will be able to run for a second full Senate term in 2020 while running for president, thanks to a law that New Jersey's governor signed in November.
California Sen. Kamala Harris, 54, joined the 2020 race on Jan. 21 with an announcement on ABC's "Good Morning America."
"I'm running for president of the United States, and I'm very excited about it," Harris, D-Calif., said on Martin Luther King Jr. Day.
Harris has broken many barriers in her career as she's served as California's attorney general and the San Francisco city attorney. She was elected to the U.S. Senate in 2016.
Since she joined the Senate, Harris has worked to establish a national profile through her questioning of Trump's judicial nominees as she sits on the Judiciary Committee.
Sen. Elizabeth Warren, D-Mass., officially announced her 2020 presidential bid on Feb. 9.
"This is the fight of our lives. The fight to build an America where dreams are possible, an America that works for everyone. I am in that fight all the way," she told supporters in Lawrence, Mass. "And that is why I stand here today: to declare that I am a candidate for President of the United States of America."
In the announcement, she called President Trump "the latest -- and most extreme -- symptom of what's gone wrong in America."
"It won’t be enough to just undo the terrible acts of this administration. We can’t afford to just tinker around the edges – a tax credit here, a regulation there. Our fight is for big, structural change," she said to cheers from the crowd.
Warren took a major step in her political career by launching an exploratory committee for president in late December.
She made a splash on Dec. 31 when she released a campaign-style video that slams the "corrupt" government, making an appeal to her party's base.
"[The government] has been bought and paid for by a bunch of billionaires and giant corporations that think they get to dictate the rules that affect everyone," Warren tells supporters, adding, "that’s not how the government is supposed to work. You know it. I know it. And we know it is time to fight back."
Warren, who was reportedly a registered Republican well into her 40s, already tested out a stump speech in Sioux City, Iowa, telling a crowd in the first-in-the-nation caucus state "we need to make a structural change."
“We need to return politics to the people,” Warren said at the Jan. 4 event.
“I can’t stop Donald Trump from what he’s going to do, I can’t stop him from hurling racial insults, I don’t have any power to do that, but what I can do is I can be in this fight for all of our families,” she added.
The 69-year-old previously taught law at Harvard University. When Warren was hired at the Ivy League school in the early 1990s, there were only 60 tenured female professors, according to The Daily Beast. According to Harvard, Warren has written more than 100 educational articles and ten books. She’s also been awarded several teaching awards — at least two from Harvard.
Warren has also been a vocal critic of Wall Street — originally conceiving what became the government's Consumer Financial Protection Bureau.
Former President Barack Obama appointed Warren to serve as assistant to the president and special advisor to the secretary of the treasury on the Consumer Financial Protection Bureau in September 2010. Warren burst onto the national scene during the financial crisis with calls for greater consumer protections. She quickly became one of the party's more prominent liberals even as she sometimes fought with Obama administration officials over their response to the market turmoil.
Former Maryland Rep. John Delaney was the first person — by far — to announce his 2020 campaign. Delaney announced his intent to run for president in July 2017, just six months into Trump's presidency.
“I'm running for President,” Delaney, a wealthy former bank executive, tweeted on July 28, 2017.
Delaney, who is socially liberal, emphasized his pro-business views in his announcement.
“We need to encourage a more just and inclusive form of capitalism and reduce barriers to small-business formation, start-ups, job creation, investment and growth,” Delaney said.
He has already invested considerable time and money in Iowa and New Hampshire.
Former Housing and Urban Development Secretary Julian Castro is hoping to make history as the country's first Latino president. Castro, who served under Obama, announced his campaign for president in his hometown, San Antonio, on Jan. 12.
"I’m running for President because it’s time for new leadership and to make sure opportunities I had are available to every American," he said during his announcement speech, which focused on immigration.
Castro, the grandson of a Mexican immigrant, mocked Trump for claiming that the U.S. faces an "invasion" from its ally to the south. "He called it a national security crisis," Castro said. "Well, there is a crisis today. It's a crisis of leadership. Donald Trump has failed to uphold the values of our great nation."
Castro, 44, became San Antonio's youngest-ever city councilman in 2001 at just 26 years old, The Atlantic Journal-Constitution reports. Years later, he became the city's mayor, serving from 2009 to 2014. During that time, he was thrust into the limelight. In 2012, he delivered the Democratic National Convention keynote speech, leading political pundits to grant him the nickname "Latino Barack Obama," according to the Texas Tribune.
The Stanford University and Harvard Law School graduate was in the running to become Hillary Clinton's potential presidential running mate but ultimately lost to Virginia Sen. Tim Kaine.
New York Sen. Kirsten Gillibrand, an outspoken Trump critic, announced the formation of a 2020 exploratory committee during a Jan. 15 appearance on "The Late Show with Stephen Colbert." It was a surprise to some who believed Gillibrand would instead opt to finish her 6-year term in the Senate.
"I'm filing an exploratory committee for president of the United States, tonight," Gillibrand told host Stephen Colbert. "I'm going to run for president of the United States because as a young mom, I'm going to fight for other people's kids as hard as I would fight for my own -- which is why I believe health care should be a right, not a privilege."
Days after the announcement, the 52-year-old will head to Iowa for a meeting and fundraiser with local Democrats, Fox News learned.
Democrat Richard Ojeda, a retired Army paratrooper and West Virginia lawmaker, formalized his campaign for the presidency on Veterans Day 2018. He announced he was going to resign his state Senate seat on Jan. 12 to focus on campaigning for president in 2020.
The so-called "Trump Democrat," who has been branded as a "JFK with tattoos and a bench press" by Politico Magazine, is of Mexican descent and became a champion of teachers during their fight for better pay and benefits. He sponsored successful legislation to make medical marijuana legal and has stressed health care and economic issues.
Ojeda came under fire in September 2018 for allegedly threatening state delegate Rupie Phillips, writing in a Facebook message, "When I'm done with you, you will beg me to ease up. I’m going to make you famous… and it’s not going to be in a good way."
At the time, the Ojeda campaign didn't deny the message was sent but pushed back against its meaning.
“This is absurd and obviously not a threat of physical violence,” the campaign’s spokeswoman told Fox News. “Richard was speaking about exposing Del. Phillips for his corruption in the West Virginia legislature."
Democratic Rep. Tulsi Gabbard of Hawaii is also planning to run for president in 2020.
"There are a lot of reasons for me to make this decision,” Gabbard told CNN on Jan. 12, though she plans to make a more formal announcement within the week. “There are a lot of challenges that are facing the American people that I'm concerned about and that I want to help solve.”
The 37-year-old Iraq War veteran, who served two tours of duty in the Middle East, is the first Hindu elected to Congress and the first member born in the U.S. territory of American Samoa. She has visited early primary and caucus states New Hampshire and Iowa in recent months and has written a memoir that’s due to be published in May.
The lawmaker made news during the 2016 presidential campaign when she opted to back Sanders instead of Clinton.
“As a veteran of two Middle East deployments, I know first hand the cost of war,” Gabbard explained in a YouTube video in February 2016, per The New York Times. “I know how important it is that our commander-in-chief has the sound judgment required to know when to use America’s military power and when not to use that power.
“As a vice chair of the D.N.C., I am required to stay neutral in Democratic primaries, but I cannot remain neutral any longer. The stakes are just too high. That’s why today I’m endorsing Senator Bernie Sanders to be our next president and commander in chief of the United States," she concluded.
Gabbard’s run would not be without controversy.
In 2016, she alarmed fellow Democrats when she met with Donald Trump during his transition to president and later when she took a secret trip to Syria and met with President Bashar Assad, who has been accused of war crimes and genocide. She questioned whether he was responsible for a chemical attack on civilians that killed dozens and led the U.S. to attack a Syrian airbase.
She said she doesn’t regret the trip and considers it important to meet with adversaries if “you are serious about pursuing peace.” She also noted that the 2003 invasion of Iraq was based on faulty intelligence and said that she wanted to understand the evidence of the Syria attack.
Fox News' Adam Shaw, Kaitlyn Schallhorn, Madeleine Rivera, Alex Pappas, Lukas Mikelionis and The Associated Press contributed to this report.