From a building in Miami set up as a processing center in 1962 for Cuban refugees fleeing Fidel Castro’s regime, Sen. Marco Rubio, the son of Cuban immigrants, announced that he is running for president.

The Florida Republican, who at 43 years old is the youngest in the field of declared presidential candidates so far, pledged to defend the American Dream, which is the title of his recently released book.

“Here in America my father became a bartender…my mother..a cashier,” Rubio, sounding at times emotional, told a crowd that often broke into applause and cheers. “ They never made it big, but they were successful. [They] gave all four of their children a life better than their own. My parents achieved what came to be known as the American Dream.”

“I’ve heard…that I should step aside and wait my turn, but I cannot," said Rubio.

I know my candidacy might seem improbable to some watching from abroad. After all, in many countries, the highest office in the land is reserved for the rich and powerful. But I live in an exceptional country. ... where even the son of a bartender and a maid can have the same dreams and the same future as those who come from power.

— Sen. Marco Rubio, announcing that he is running for president

He said he must run now because too much is at stake for the country, and “I can make a difference as president.”

“This isn’t just a country where I was born. America is a place that literally changed my family’s history."

In the Freedom Tower, known as “the Ellis Island of the South, Rubio said the American Dream is slipping from too many families' grip, and young Americans face unequal opportunities to succeed.

It was a message honed to pitch the GOP as a party that cares about all voters, not just those in upper tax brackets.

He told supporters, "The time has come for our generation to lead the way toward a new American century."

Rubio's remarks came as former Secretary of State Hillary Clinton was traveling to Iowa on her first trip as a candidate. Her entrance into the race with an online video Sunday was seen by some political experts as potentially robbing some attention from Rubio's splash into the race.

But Rubio saw an opportunity to cast the presidential contest as one between a fresh face representing a new generation of leadership and familiar faces harking back decades — namely, the 67-year-old Clinton and 62-year-old Jeb Bush, the former Florida governor who long has been seen as Rubio's mentor.

"While our people and economy are pushing the boundaries of the 21st century, too many of our leaders and their ideas are stuck in the 20th century," Rubio said to applause.

The swipe at Bush was implied; with Clinton, he was more direct.

"Just yesterday, a leader from yesterday began a campaign for president by promising to take us back to yesterday," Rubio said to jeers. "Yesterday is over and we are never going back."

As U2 songs reverberated around the meeting hall, Miami Mayor Tomas Regalado called Rubio's announcement one of the most historic moments in city history.

"Freedom Tower symbolizes what the American Dream means to the Cuban exile community," Regalado said. "His announcement will resonate throughout the nation and throughout the world."

Rubio threw his hat in a ring expected to be crowded with presidential candidates from his party, including Bush, someone whom many assumed Rubio would not run against for the party’s nomination.

Bush long was described as Rubio’s mentor, leading many political observers, including fellow Florida Republican and Cuban-American Rep. Ileana Ros-Lehtinen, to say that the junior senator would set aside presidential aspirations if the former governor decided to run.

Described by many as a young man in a hurry, Rubio will no doubt hear rivals tell voters he's not ready for the White House.

Hours before his rally, the chairwoman of the Democratic National Committee, Rep. Debbie Wasserman Schultz of Florida, criticized Rubio as just another establishment Republican with no new ideas.

"He's a follower, peddling the same tired Republican playbook," she told reporters. "Marco Rubio has pandered to the Republican base throughout his whole career."

To counter views of him as a neophyte, Rubio has outlined specific policy proposals both on foreign and domestic issues. Earlier this year, Rubio said that senators are better prepared than governors to be president given their work on foreign policy.

On Tuesday, during his first day as a candidate, he is set to return to Washington to join a Senate hearing on a proposed deal with Iran on its nuclear ambitions.

"The Republican Party, for the first time in a long time, has a chance in this election to be the party of the future," Rubio told his donors earlier on Monday, referring to Clinton. "Just yesterday, we heard from a leader from yesterday who wants to take us back to yesterday, but I feel that this country has always been about tomorrow."

Rubio faces steep challenges to winning the nomination, one of them from his Bush. Rubio would become the third major GOP contender to declare himself a candidate, after Texas Sen. Ted Cruz and Sen. Rand Paul, in a field that could grow to 20 or more candidates.

A first-generation immigrant whose parents fled Cuba, Rubio could make history as the nation's first Hispanic president (as could Cruz). Rubio is expected to stress himself as the embodiment of American opportunity, as the son of a maid and bartender who worked his way through law school and now sits in Congress.

"I know my candidacy might seem improbable to some watching from abroad," Rubio said at the Freedom Tower. "After all, in many countries, the highest office in the land is reserved for the rich and powerful."

"But I live in an exceptional country. ... where even the son of a bartender and a maid can have the same dreams and the same future as those who come from power."

The Associated Press contributed to this report.

Francisco Alvarado, a freelance journalist in Florida, contributed to this report.

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