PHILADELPHIA ― The Democratic Party officially nominated Virginia Sen. Tim Kaine to be its vice presidential candidate on Wednesday.

Kaine, who served as the governor of the Commonwealth of Virginia and as the chair of the Democratic National Committee before following fellow former Virginia Gov. Mark Warner to the Senate in 2013, emerged as the favorite to become former Secretary of State Hillary Clinton’s running mate in the weeks before the Democratic National Convention. One clear attribute Kaine brings to the ticket is electability ― he has never lost an election in his 22-year political career.

That he came up through the ranks in Virginia, which has been trending Democratic in recent election cycles but remains a competitive state in presidential elections, is also thought to be one of Kaine’s key attributes. As a bullish Larry Sabato, who runs the University of Virginia’s Center for Politics, wrote in the Washington Post, “[With] Kaine on the ticket, Virginia can probably retire its swing state jersey for this year.”

In picking Kaine, Clinton hopes to further define her candidacy as hopeful and competent ― as well as brand her opponent, Donald Trump, as a reckless con-man. Sharing the stage for the first time as ticket-mates Saturday, Kaine tore into the GOP nominee, saying that Trump “leaves a trail of broken promises and wrecked lives wherever he goes.” For her part, Clinton referred to her new running mate as “everything Donald Trump and Mike Pence are not,” as well as “a progressive who likes to get things done.”

But it will be convincing the liberal base of the Democratic Party that Kaine is just such a progressive that will be the tough sell. Backers of Clinton’s primary opponent, Bernie Sanders, who were looking to Clinton’s vice-presidential pick as a signal that their policy preferences would have a home in a Clinton White House, were disappointed that Kaine ended up being her choice.

Kaine’s supporters were quick to point out that he’d fought tirelessly to end racial discrimination in housing, had faced down the gun lobby in a pro-gun state and earned stellar endorsements from reproductive rights groups after an early career in which he’d mostly earned their skepticism. But in the weeks leading up to Clinton’s selection, Kaine broke with the party’s liberal base in two significant ways: withholding his signature from a letter organized by his Democratic colleagues that would call for tougher regulations on payday lenders, while putting his name to another letter that would allow large regional banks to skate on capitalization requirements.

Should Clinton win the election, Kaine would become the third vice president from the Commonwealth of Virginia ― the first since John Tyler in 1841.

CORRECTION: An earlier version of this post said Kaine was nominated Tuesday. It happened Wednesday.