Hillary Clinton formally introduced Tim Kaine on Saturday afternoon as her running mate at Florida International University in Miami.

It was the first time the two appeared together as a political ticket.

Clinton praised Kaine as a progressive who also knows how to reach across the aisle to get things done.

The former New York senator Kaine's his tenure as a legislator fighting for causes such as public education funding, more gun control, and LGBT rights.

After the 2007 Virginia Tech massacre, Kaine drew notice in his anti-NRA push for tighter gun laws.

Both Democrats targeted Republican Party Nominee Donald Trump as the doom and gloom candidate who does not understand how democracy works.

"So while Tim was taking on housing discrimination and homelessness, Donald Trump was denying apartments to people who were African-Americans," Clinton said at the introductory conference.

"When Donald Trump says he has your back, you better watch out. From Atlantic City to his so-called university, he leaves a trail of broken promises and wrecked lives where ever he goes," Kaine said when he took the podium. "Hillary Clinton is the direct opposite of Donald Trump."

Ending the waiting game, in a tweet to supporters Friday night, Hillary Clinton announced her running mate:

She then tweeted a link to video featuring her and Kaine on the campaign trail.

The much-anticipated announcement of Kaine comes just three days before Democrats head to Philadelphia for their convention.

Kaine is the current senator from Virginia. He previously served as governor of that state and also chaired the Democratic National Committee.

Clinton was asked about Kaine as a possible running mate during a PBS interview last week.

"He's never lost an election. He was a world-class mayor, governor and senator, and is one of the most highly-respected senators I know," she said.

Earlier this month, Kaine campaigned with Clinton in Virginia, previewing what the Democratic ticket would look like.

"Donald Trump trash talks women. He trash talks folks with disabilities," Kaine said.

Kaine was considered by some to be the safe choice, but he is not terribly popular with the progressive wing of the party.

He is a supporter of free-trade agreements, including NAFTA and the TPP, which critics, including Clinton's former rival Bernie Sanders, claim send American jobs overseas.

An opponent of the death penalty, Kaine still allowed 11 executions as governor.

But the pick of Kaine appears to be aimed more at middle-of-the-road voters than liberals, and pulling independents away from Trump.

"Do you want a trash-talker president or a bridge-builder president? That's what's at stake," Kaine said.

Another benefit with Kaine is that he speaks Spanish. Observers say Trump has already alienated many Hispanic-Americans with his anti-immigrant rhetoric. But Kaine on the Democratic ticket is now literally speaking those voters' language.

In a statement, a spokesperson for the Trump campaign said, "The choice has never been clearer - Donald Trump calls on us to Believe in America, while the Status Quo ticket of Clinton-Kaine wants us to believe in a rigged system that enriches them at your expense."

Trump himself took to Twitter on Friday night:

"Bob M" is likely referring to former Virginia Gov. Bob McDonnell, who was convicted in 2014 of doing favors for businessmen in exchange for gifts and money.

The Supreme Court overturned his conviction last month, saying he did not violate federal bribery laws.

A lower court will decide whether he gets another trial.

Clinton and Kaine respond by saying Trump is a heartless wanna-be dictator, who boasted Thursday at the Republican National Convention that he alone can fix America's problems.

"That is not a democracy," Clinton said Saturday. "We fought a revolution because we didn't want one man making all the decisions for us."

Clinton and Kaine are set to give their first joint interview on CBS's "60 Minutes" Sunday night.

Monday night, Democrats will kick off their convention in Philadelphia. Both New York City Mayor Bill de Blasio and New York Gov. Andrew Cuomo are expected to have speaking roles.

Clinton is expected to formally accept the nomination of her party with a speech Thursday night.