Hillary Clinton is expected to announce her vice presidential running mate on Friday, and Virginia Sen. Tim Kaine has reportedly emerged as the front-runner.

Sources told Fox News the presumptive Democratic presidential nominee has not told Kaine or two others believed to be on her short list who has been eliminated. The Wall Street Joual reported Friday moing that Clinton is believed to be poised to choose Kaine.

In addition to Kaine, Clinton is reportedly considering Agriculture Secretary Tom Vilsack and New Jersey Sen. Cory Booker -- a late entry.

Kaine, who is also a former Virginia goveor and former chairman of the Democratic National Committee, is seen by many Democrats as a more moderate candidate with swing-state appeal. He was considered one of President Obama’s top three finalists for the position in 2008.

Kaine endorsed Clinton early on in the campaign, and is also generally regarded as a safe pick for the former secretary of state. He also speaks fluent Spanish which could be useful in increasing the campaign’s reach among Hispanic voters.

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Kaine's stance on certain foreign policy issues could prove problematic to her campaign as she seeks to motivate the party’s base. Kaine has criticized Obama’s approach to Syria, and has pushed repeatedly for a formal authorization for military action against ISIS.

The expected announcement will be just days in advance of the opening of the Democratic convention in Philadelphia on Monday. Republican nominee Donald Trump followed a similar strategy, tweeting out his vice presidential choice of Indiana Gov. Mike Pence on the Friday before the Republican convention.

Booker, a Yale Law School graduate, was among the first prominent Democratic lawmakers to endorse Clinton. He said he would be willing to serve if chosen.

“I know the Clinton campaign is in the midst of deciding. I’m very happy to be where I am,”  the first-term senator and former mayor of Newark, told reporters in Cleveland.

Vilsack, a former Iowa goveor who is a longtime friend of the Clintons, could help with the male vote.

After calling her VP pick, Clinton was expected to inform supporters via an email blast, to avoid a leak.

Clinton, who will be in Florida Friday, is trying to strike the right balance with the base as she weighs her running mate options, after a rigorous primary battle against progressive Vermont Sen. Beie Sanders, who only recently endorsed Clinton.

Clinton also has met with several other prospects, including Massachusetts Sen. Elizabeth Warren, Colorado Gov. John Hickenlooper, Labor Secretary Tom Perez and Housing Secretary Julian Castro.

Fox News’ Mike Emanuel, Jason Donner and Jennifer Griffin contributed to this report.