Donald Trump has officially started vetting potential vice president picks with sources close to the campaign telling the Washington Post former opponent, New Jersey Gov. Chris Christie is a front-runner along with former speaker of the house Newt Gingrich.

Sources close to the Trump campaign and the vice president selection process told the Washington Post that serious contenders like Christie and Gingrich have been asked to submit documents. Attorney Arthur B. Culvahouse Jr. asked the two for their tax records and articles or books they've published reported the Washington Post. In addition to submitting the documents Christie and Gingrich were also asked to answer over 100 questions.  

The Washington Post reported the information about the VP search came from five people close to the process who wished to remain anonymous "to discuss private conversations with campaign officials."

GOP presidential candidate Ben Carson, who once said he'd be open to running as Trump's vice president, is one of those in Trump's circle who favors Gingrich reported the Washington Post.

Besides Christie and Gingrich sources told the Washington Post there were other candidates being discussed.

Those candidates include Alabama Senator Jeff Sessions, Tennessee Senator Bob Corker, and Indiana Governor Mike Pence. However, the Washington Post reported it's unclear how extensively they're being vetted. Even Trump's other opponent Ted Cruz has come up as an option despite Cruz refusing to endorse Trump. Trump's campaign has reportedly been trying to contact Cruz's people for a makeup between the two.

In a "Fox News Sunday" interview this past weekend Gingrich said he hasn't been contacted by the Trump campaign when asked if he was being vetted.

"I think Donald Trump does not want to make a decision until the convention," he said. "I think that he is a very decisive person and in case of a few of us—I'm an example. There's not much vetting to do."

Last month Trump's campaign chairman Paul Manafort told The Huffington Post in an interview that women or minorities weren’t being considered for VP because he thought it’d seem like “pandering."

"He needs an experienced person to do the part of the job he doesn’t want to do," Manafort said. "He seems himself more as the chairman of the board than even the CEO, let alone the COO."