Heidi M. Przybyla

USA TODAY

Sen. Tim Kaine of Virginia is Hillary Clinton’s pick to be her running mate on the Democratic Party’s ticket for the White House, the presumptive Democratic presidential nominee announced Friday on Twitter.

Kaine, a former governor, has "devoted his life to fighting for others," Clinton’s announcement said.

The 58-year-old Kaine had been the focus of increasing speculation in recent days, as Clinton insiders said that former President Bill Clinton, the presumptive nominee’s husband, was backing Kaine.

The Clinton team has been high on Kaine from the start because of his extensive governing experience — he is a former governor, lieutenant governor and Richmond mayor. Clinton’s pick reflects a calculation that she needs a candidate who will be in a strong position to govern versus a progressive firebrand to help her rev up Democratic base voters. As a member of the Armed Services and Foreign Relations committees, Kaine would add to the Democratic ticket's national security credentials given Clinton's tenure as secretary of State.

The pick was believed to have been made earlier in the day Friday, but it was delayed after reports of a mass shooting in Munich that claimed at least eight lives.

Clinton and Kaine will campaign together for the first time in an appearance in Miami after solo appearances in Orlando and Tampa on Friday. The Florida events come ahead of the Democratic National Convention, which kicks off Monday in Philadelphia.

The presumptive Democratic nominee had weighed whether she needed a more outspoken liberal on her ticket to satisfy the Bernie Sanders wing of the party. Yet with polls showing Sanders voters moving toward her and given Republican Donald Trump's pick of Indiana Gov. Mike Pence, a strong conservative, as his running mate, strategists say Clinton had more freedom to pick a conventional swing state candidate such as Kaine.

The choice signals a tactical decision to make a strong play for independent and moderate voters, said Matt Bennett, senior vice president at Third Way, a centrist Democrat policy group. “Conventional wisdom says presidential elections are all about base turnout,” he said in an email. “Secretary Clinton has rejected that approach, picking a sensible, swing-state centrist. She clearly believes that the way to win in a divided country and to govern in a divided Washington is by making the tent bigger and appealing to common interests.”

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With her running mate announcement, Clinton hopes to seize the campaign spotlight back from Trump and Republicans who capped off their convention Thursday with Trump accepting the GOP nomination — a milestone the Clinton campaign highlighted in a bid to rally supporters.

"This is real — Donald Trump just accepted the @GOP nomination," the campaign tweeted, urging supporters to retweet the message if they agreed "we can't let him become president."

The GOP convention highlighted the aggressive posture Republicans are likely to take against Clinton in the fall campaign, as delegates throughout the four-day gathering chanted "lock her up" when the former secretary of State's name was mentioned.

Kaine is a safe pick who may also be able to bring in more white male support — and he was already vetted by Barack Obama’s team in 2008 (he was an early supporter of the then-Illinois senator during his primary campaign with Clinton). Kaine and Clinton took a test run during an appearance together in northern Virginia on July 14.

Kaine is also fluent in Spanish and a strong advocate of overhauling the immigration system — both assets as Clinton counts on a strong Hispanic voter turnout, given GOP nominee Donald Trump's controversial statements about Mexican immigrants and proposed wall along the southern border. The two are expected to campaign together for the first time Saturday in an appearance in Miami.

Another advantage for the Democratic Party with Kaine's selection: Virginia’s current governor, Terry McAuliffe, a Democrat, would appoint another member of the party to fill Kaine’s seat.

Still, Kaine has liabilities, particularly with progressives. Kaine cut deals with a Republican legislature as Virginia governor and supported the Trans-Pacific Partnership, which Clinton now says she opposes. As a Catholic, Kaine personally opposes abortion, although he’s voted to protect abortion rights.

In any other recent presidential cycle, Kaine’s more moderate profile would be considered an asset. But Sanders has warned he will hold Clinton to account on several progressive campaign pledges she’s taken, and Kaine’s pick may not be reassuring as she seeks to shed the Wall Street label.

"The mood of the country is a populist one,” said Stephanie Taylor, co-founder of the Progressive Change Campaign Committee in reacting to the decision. “Republicans will run hard against Democrats on trade this year. Unfortunately, since Tim Kaine voted to fast track the Trans-Pacific Partnership, Republicans now have a new opening to attack Democrats on this economic populist issue.”

The Trump campaign also criticized the decision. "It's only fitting that Hillary Clinton would select an ethically challenged insider like Tim Kaine who's personally benefited from the rigged system," Trump spokesman Jason Miller said in a statement.

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Kaine may also not be the kind of attack dog Clinton had wanted to combat Trump. On NBC’s Meet the Press, Kaine recently acknowledged that “I am boring.” Even so, in his recent Virginia appearance, Kaine tried to show his ability to go on the offensive. He offered his own frame for Trump, saying he would be the “you’re-fired president,” a “trash talker” and the “me-first president."

Kaine is also younger than others Clinton was considering, especially important as the Democratic Party looks to elevate a younger group of Democrats as possible successors if Clinton wins. A Harvard Law School graduate, Kaine comes from a working class family – his father was welder – and grew up in the Kansas City area of Missouri.

A campaign statement also highlighted Kaine's work as a Jesuit missionary in Honduras, his experience as a lawyer representing people against housing discrimination due to race or disabilities and his signature, as governor, of an executive order restricting access to firearms for persons adjudicated mentally ill.

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Contributing: Jason Noble, The Des Moines Register