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MIAMI — Hillary Clinton must be feeling good about her choice of Tim Kaine after her brand new running mate brought a packed house to its feet here Saturday during the first joint outing for the 2016 Democratic ticket.

Kaine has described himself as “boring,” but he delighted a crowd of 5,000 at Florida International University with his fluency in Spanish and attacks on Donald Trump, boosted by the fact that Clinton has not visited the area since the Florida primary in April.

And while Bernie Sanders supporters are condemning Kaine's selection and fuming over leaked Democratic National Committee emails that show an apparent attempt to damage Clinton's primary rival, the only sign of dissent was a small protest that quickly petered out.

“Sen. Tim Kaine is everything Donald Trump and Mike Pence are not. He is qualified to step into this job and lead on day one,” Clinton said as she introduced her new vice presidential pick, who was announced Friday night.

“And he is a progressive who likes to get things done. That’s my kind of guy,” Clinton added.

Kaine comes across as affable and unassuming, a quality allies say voters might find refreshing in an election year dominated by negative rhetoric. And Clinton said he’s also tougher than he looks.

“Make no mistake, behind that smile, Tim has a backbone of steel," she said. "Just ask the NRA.”

The nearly leak-free rollout of Kaine could hardly have been more different than Trump’s of Indiana Gov. Mike Pence last week. There was no revisiting of the primaries, no semi-public prevarication, and no awkward logos.

Vice presidential candidate Sen. Tim Kaine waves with his presidential running mate Hillary Clinton after she introduced him during a campaign rally in Miami on July 23. SCOTT AUDETTE / Reuters

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And the choice of a highly diverse campus in a highly diverse city and critical battleground state for the introduction rally was no accident.

Kaine broke into Spanish almost immediately, saying, "Companeros de alma in this great lucha ahead” — "We are soulmates in this great fight ahead."

That skill could be a major asset for Democrats as they hope to drive up their margin with Latinos against Trump to historic levels.

Meanwhile, Republicans opened four lines of attack on the new VP nominee: That Kaine is too much of an insider, that he’s tainted by gifts he accepted as governor of Virginia, that he supported the Trans Pacific Partnership and that he’s unacceptable to the Sanders wing of the party.

“Hillary Clinton’s choice of Tim Kaine does nothing to unify a fractured Democrat base which is repelled by her dishonesty and cronyism,” said Republican National Committee Chairman Reince Priebus.

Trump didn't hold back either, tweeting Saturday after seeing the pair together that "ISIS and our other enemies are drooling. They don't look presidential to me!"

Just saw Crooked Hillary and Tim Kaine together. ISIS and our other enemies are drooling. They don't look presidential to me! — Donald J. Trump (@realDonaldTrump) July 23, 2016

Bernie Sanders and Elizabeth Warren, the two most prominent leaders of the liberal wing of the Democratic Party, have been silent on the Kaine pick in the hours since it was announced.

Kaine acknowledged that most in the audience had probably never heard him speak. “Let’s be honest, for many of you, this is the first time you heard my name,” he said.

And the former Virginia governor introduced himself in a way that emphasized his similarities with Clinton.

Both were raised in the Midwest (Clinton in Illinois, Kane was born in Minnesota and raised in Kansas). Both left elite law schools (Clinton at Yale and Kaine at Harvard) for public service (Clinton to the Children's Defense Fund, Kaine to be a missionary in Honduras).

Both have spouses in politics (Clinton’s was a former president, Kaine’s is Virginia’s secretary of education).

And both are public about their faith. "I’m a Catholic, and Hillary is a Methodist, but I tell you, her creed is the same as mine: Do all the good you can,” Kaine said.

Both also earn some of the same praise from boosters (experienced, competent, moderates) and criticism from detractors (pliant, uninspiring, insiders).

Kaine noted that his son is a Marine who is deploying to Europe in a few days to "uphold America's commitment to our NATO allies.” Trump has questioned the value of that alliance.

“That's an open invitation to Vladimir Putin,” Kaine said, going on to suggest Trump was doing Putin’s bidding.

And Kaine got quiet as he recalled being governor during the Virginia Tech massacre in April 2007, saying it was the worst day of his life.

Campaign aides also gave new details about the cloak and dagger maneuvers behind Kaine’s selection.

Kaine found out about his selection at 7:32 p.m. Friday night when Clinton called him, according to aides, while he was attending a fundraiser in an old shipyard in Newport, Rhode Island. He snuck into an office to take the call as staff fended off dockworkers trying to get in.

Just got off the phone with Hillary. I’m honored to be her running mate. Can’t wait to hit the trail tomorrow in Miami! — Senator Tim Kaine (@timkaine) July 23, 2016

Clinton told him there was a plane waiting at the airport and that campaign chairman John Podesta and a team from the Brooklyn headquarters was sitting in a car parked nearby. They had slipped out of Clinton’s Brooklyn office using a freight elevator.

With a large scrum of reporters waiting outside, Kaine first attempted to escape the fundraiser by boat, but opted for a Volvo instead and made it back to the Viking Hotel undetected. Aides got to work right away on the speech, with the senator contributing, but he never got a chance to practice it out loud before delivering it.

On the way to the airport, Kaine received a congratulatory call from President Barack Obama. He celebrated with a glass of champagne in the air.