Hillary Clinton and running mate Virginia Sen. Tim Kaine kicked off their first official campaign appearance together Saturday by pitching themselves as the polar opposite of Republican nominee Donald Trump and his running mate Mike Pence.

Wasting no time targeting Trump, Kaine asked the Miami crowd, “Do you want a ‘you’re fired’ president or a ‘you’re hired’ president? Do you want a trash-talking president or a bridge-building president?”

Speaking in Spanish at times, Kaine drew comparisons between the Democratic ticket and Trump. Playing off the Republican nominee's "Make America Great Again!" slogan, Kaine asked, "Isn't it great already?"

Clinton introduced Kaine as “a progressive who likes to get things done” and added the former Virginia governor cares more about making a difference than making headlines.

She also called herself and Kaine “everything that Donald Trump and Mike Pence are not."

But Clinton’s campaign faced mounting unrest from some liberal groups and supporters of Vermont Sen. Bernie Sanders over her choice of running mate. Kaine has been bashed by some who says he’s too conservative on issues like abortion and trade deals. 

Shortly after Friday's announcement that Kaine was Clinton's pick, Stephanie Taylor of the Progressive Change Campaign Committee said the senator's support for the Trans-Pacific Partnership trade pact gives Republicans "a new opening to attack Democrats on this economic populist issue."

Notably, a campaign aide said Kaine made clear "in the course of discussions" that he shares Clinton's opposition to TPP in its current form.

Sanders supporters have vowed to show up in droves for half a dozen sanctioned protests near Philadelphia's Wells Fargo Center when the convention kicks off on Monday.

Sanders also plans to meet with 1,900 of his delegates before the start of the convention.  

Clinton offered Kaine the vice presidential spot on the Democratic ticket in a phone call on Friday night. His selection completes the line-up for the general election, in which Clinton and Kaine will face off against Trump and Pence.

Kaine, 58, was long viewed as a likely choice, a former governor of politically important Virginia and mayor of Richmond who also served as chairman of the Democratic National Committee.

The bilingual Kaine is also likely to be a valuable asset in battleground states like Florida, as the Clinton campaign appeals to Hispanic-Americans turned off by Trump's harsh rhetoric about immigrants.

He also had a particularly powerful backer: President Obama, who advised Clinton's campaign during the selection process that Kaine would be a strong choice.

News that Kaine was Clinton's pick was greeted warmly by some Republicans Friday evening. 

"Trying to count the ways I hate (at)timkaine," Arizona Sen. Jeff Flake wrote on Twitter. "Drawing a blank. Congrats to a good man and a good friend.”

Kaine was the choice over Agriculture Secretary Tom Vilsack, a longtime friend of the candidate and former President Bill Clinton.

Clinton's campaign teased the announcement throughout Friday, encouraging supporters to sign up for a text message alert to get the news -- a favorite campaign method for getting contact information about voters.

The Democratic candidate made no mention of her impending pick during a somber meeting with community leaders and family members affected by the Pulse nightclub shooting in Orlando and a later campaign rally in Tampa.

When the news came via text, she quickly followed it with a message on Twitter: "I'm thrilled to announce my running mate, (at)TimKaine, a man who's devoted his life to fighting for others."

Trump also announced the choice of his running mate on Twitter, and followed it up with an announcement the next day at a hotel in midtown Manhattan -- a curious choice given New York City's strong Democratic history.

Before entering politics, Kaine was an attorney who specialized in civil rights and fair housing. He learned Spanish during a mission trip to Honduras while in law school. During his political career, he's demonstrated an ability to woo voters across party lines, winning his 2006 gubernatorial race with support in both Democratic and traditionally Republican strongholds.

His wife, Anne Holton, is the daughter of a former Virginia governor and is herself a former state judge and the state's education secretary. The couple has three children.

Trump, in a text to his own supporters, said Obama, Clinton and Kaine were "the ultimate insiders" and implored voters to not "let Obama have a 3rd term.”

Kaine got some practice challenging Trump's message when he campaigned with Clinton last week in northern Virginia, where he spoke briefly in Spanish and offered a strident assault on Trump's White House credentials.

The Associated Press contributed to this report.