WASHINGTON –

Republican stalwarts Newt Gingrich and New Jersey Gov. Chris Christie are at the top of Donald Trump's short list to be his vice presidential running mate, sources said, but the real estate developer is casting a wide net.

With less than three weeks to go until he is formally nominated at the Republican National Convention as the party's candidate in the Nov. 8 election, Trump's search for a No. 2 has intensified. The wealthy businessman, a political neophyte, has said he wants a political veteran to help him navigate the power corridors of Washington.

Gingrich and Christie, both loyal to Trump at a time when many Republican colleagues want nothing to do with him, would meet the New Yorker's requirement for experience — but would come with pluses and minuses.

Other names to watch include three senators — Bob Corker of Tennessee, Joni Ernst of Iowa and Jeff Sessions of Alabama — and two governors, Mike Pence of Indiana and Mary Fallin of Oklahoma, Republicans close to the campaign said.

Trump has set up a meeting with Pence this weekend, a spokesman for the governor said on Friday. He has also met with Corker and Fallin.

"Mr. Trump is meeting with a number of Republican leaders in the run-up to the convention in Cleveland, and he has a good relationship with Gov. Pence," Trump spokesman Jason Miller said in an email response to a question from Reuters.

The businessman's campaign has tried to bring in experienced political hands, including adding Republican pollster Kellyanne Conway on Friday, amid a series of departures.

Trump fired campaign manager Corey Lewandowski in June. This past week, the campaign lost Kevin Kellems, a recent hire who oversaw political surrogates who back Trump, according to a resignation email seen by Reuters.

An experienced running mate also could help with fundraising. Hillary Clinton, the presumptive Democratic nominee, raised more than $40 million for her campaign in June and about $28 million for the party. Trump, who largely funded his primary run himself, has not yet released his June fundraising numbers.

Trump is expected to name his running mate close to the July convention, which he said on Friday would be a "great time." Trump told a conservative gathering in Colorado that his children and his wife, Melania, would speak in Cleveland.

Gingrich, who was speaker of the House of Representatives in the 1990s and ran for president in 2012, is a popular conservative writer and speaker, and has been an important behind-the-scenes voice in urging Trump to adopt a more presidential demeanor.

But because Trump is 70 and Gingrich is 73, they could face difficulty in appealing to a younger generation.

Christie quickly endorsed Trump after dropping out of the race early this year. A source said the 53-year-old has emerged as a key adviser to Trump and his campaign team at Trump Tower. A source said Christie was instrumental in coaxing Trump to take a less confrontational stance with a Mexican-American federal judge overseeing a fraud case involving the candidate's now-defunct Trump University venture.

One clue to Christie's rising importance came this past week when a group of campaign supporters held a conference call to discuss strategy and talking points for use in media appearances.

A source said that during the call Christie's name was raised as someone who might comment on former President Bill Clinton's private meeting with Attorney General Loretta Lynch. As a former federal prosecutor, Christie would be a credible voice.

The Monday night meeting of Clinton and Lynch, the top U.S. law enforcement officer, at the Phoenix airport has been criticized because Hillary Clinton is under federal investigation for her use of a private email server when she was President Barack Obama's secretary of state.

The source said campaign associates made clear that Christie was not to be used for this purpose. "They're saving him for the general election. They don't want to overexpose him," the source said.

Still, many Republicans are waiting to see whether Christie is named as an unindicted co-conspirator in a 2014 case involving charges that lanes on the George Washington Bridge were closed in New Jersey for political reasons.

Corker, 63, offers Trump deep foreign policy experience as chairman of the Senate Foreign Relations Committee and, like Trump, believes the Republican Party needs to be shaken up. His stock may have gone down, however, because he has not shied away from criticizing the candidate at times.

Ernst, a first-term senator and military veteran, could help improve Trump's standing with women. She was a tacit supporter of rival Marco Rubio during the Republican nominating campaign, though she has said she will support the party's nominee.

Ernst, who turned 46 on Friday, said in June she had not been contacted by the Trump campaign.

The same goes for Oklahoma's Fallin, who was among several Republican governors at a joint meeting with Trump in June.

"It's an honor to be mentioned for the office of vice president. I have not had any conversation with Mr. Trump about the vice presidency position," Fallin, 61, said in a statement.