The vetting is over — the hard choice has been made. And on Saturday, Hillary Clinton and Senator Tim Kaine of Virginia made their debut as a presidential ticket, offering Democrats the first glimpse of the team that will take on Donald J. Trump in the general election.
Mrs. Clinton and Mr. Kaine appeared at a 1 p.m. rally at Florida International University in Miami, showing up nearly an hour late. The joint appearance was meant to give the campaign a burst of energy as Democrats head to their national convention on Monday, starting the formal process of nominating Mrs. Clinton.
“Tim Kaine is everything Donald Trump and Mike Pence are not,” Mrs. Clinton said in introducing her running mate at the rally. “He is qualified to step into this job and lead on day one.”
The rally came a day after Mrs. Clinton announced her selection in a text message to supporters Friday night, saying that she was “thrilled to tell you this first: I’ve chosen Sen. Tim Kaine as my running mate.”
Mr. Kaine peppered his speech with Spanish, telling the crowd, “Somos Americanos todos” — “We are all Americans” — an implied dig at Mr. Trump and his attacks on immigrants.
Mr. Kaine also went after Mr. Trump more explicitly, hitting his record as a casino mogul in Atlantic City and the defunct Trump University.
“He leaves a trail of broken promises and wrecked lives wherever he goes,” Mr. Kaine said of the Republican nominee.
The rollout of his candidacy in Florida is no accident. Florida is a crucial battleground that will be hotly contested in the fall, and Mrs. Clinton is moving swiftly to press her advantage with the state’s large Hispanic electorate, many of whom have been turned off by Mr. Trump’s hard-line immigration policies.
The university is also a major melting pot, with a student population that is 61 percent Hispanic. For the Clinton campaign, it was an opportunity to showcase Mr. Kaine’s fluency in Spanish, a language he learned as a missionary in Honduras.
The conventional rollout of Mr. Kaine as vice-presidential choice comes in sharp contrast to the haphazard unveiling by Mr. Trump of Gov. Mike Pence of Indiana last week as his running mate. That was plagued by leaks, waffling and a postponed announcement that was ultimately made by Mr. Trump, now the Republican nominee, on Twitter. They held their joint appearance at a Manhattan hotel, and Mr. Trump did most of the talking.
Mrs. Clinton spent months mulling her options and also gave serious consideration to Thomas E. Perez, the labor secretary, and Senator Cory Booker of New Jersey. Ultimately she went with Mr. Kaine, who is seen as a solid and safe selection, even though some in the party’s progressive wing will be disappointed.
For Mr. Kaine, who was on President Obama’s vice-presidential shortlist eight years ago, the biggest challenge will be adjusting to the national spotlight and embracing the role of attack dog. He gave it a try last week during somewhat of an audition with Mrs. Clinton in Virginia, assailing Mr. Trump as selfish and divisive and testing out a few new searing lines.
“Do you want a trash-talker president or a bridge-builder president?” Mr. Kaine asked the crowd.
The selection sets in stone a general election contest that has two starkly different candidates at the top of the ticket, but two running mates with long government experience both in Congress and at the helm of state governments.
Mr. Trump selected as his ticket mate Mr. Pence, a former congressman with whom he had little prior relationship. He was chosen to help the New York businessman win the support of far-right conservatives who are skeptical of Mr. Trump’s social positions and to calm the nerves of establishment Republicans.
Mrs. Clinton has called Mr. Pence the “most extreme pick in a generation,” highlighting his positions against same-sex marriage and abortion rights and his support for prayer in schools.
Within hours of being tapped by Mrs. Clinton, Mr. Kaine was already taking fire from Mr. Trump, who ridiculed him on Twitter for accepting lavish gifts as governor of Virginia. The Trump campaign also unleashed a new moniker for the Democratic vice-presidential candidate: “Corrupt Kain.”
Both candidates are hopeful that their running mates will each help deliver their home states in November.
Mr. Kaine is very popular in Virginia. The state has trended Democratic in recent elections, and Mr. Obama captured it in 2008. His victory ended a decades-long losing steak for Democrats, who had not won there since Lyndon B. Johnson’s election in 1964. Mr. Kaine will be charged with ensuring that does not change.
Mr. Pence’s state, Indiana, is reliably Republican in presidential contests, although Mr. Obama narrowly carried that state in 2008. Mr. Pence will be under pressure to keep it in the red column.
Despite the buzz surrounding vice-presidential selections, the data shows that they tend to have little effect on the outcomes of general election contests.
While Mr. Kaine is well liked by the Democratic Party’s establishment, his appeal among the broader electorate remains unclear. A Monmouth University poll conducted in June found that just 9 percent of voters were more likely to back Mrs. Clinton if she picked Mr. Kaine, while 13 percent were less inclined to do so.
“At best, they can help with a specific constituency or in a key state,” Patrick Murray, of the Monmouth University Polling Institute, said of running mates. “At worst, they can demonstrate poor decision-making on the part of a person who aspires to be leader of the free world.”