WASHINGTON (Reuters) - Former House Speaker Newt Gingrich and New Jersey Governor Chris Christie top Donald Trump’s short list to be his vice presidential running mate, sources said, but the candidate is casting a wide net that also includes several U.S. senators and other governors.

With less than three weeks to go until his formal nomination 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 his requirement for experience - but would come with minuses as well as pluses.

Other names to watch include U.S. Senators Bob Corker of Tennessee, Joni Ernst of Iowa and Jeff Sessions of Alabama and Governors Mike Pence of Indiana and Mary Fallin of Oklahoma, Republicans close to the campaign said this week.

Trump has set up a meeting with Pence this weekend, a spokesman for the governor said on Friday. The New Yorker 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.

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 her party. Trump, who largely self-funded his primary run, has not yet released June fundraising numbers.

Trump is expected to name his running mate close to the July 18-21 convention.

RUNNING MATE PROSPECTS

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.

U.S. Republican presidential candidate Donald Trump and New Jersey Governor Chris Christie appear together at a fundraising event in Lawrenceville, New Jersey, U.S., Many 19, 2016. REUTERS/Mike Segar

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

Christie quickly endorsed Trump after quitting the race early this year. A source said the 53-year-old governor has emerged as a key adviser to Trump and his campaign team. A source said Christie was instrumental in coaxing Trump to be less confrontational with a Mexican-American federal judge overseeing a fraud case involving Trump.

One clue to Christie’s rising importance came earlier this week when some campaign supporters held a conference call to discuss strategy and talking points for 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 meeting earlier this week with Attorney General Loretta Lynch. As a former federal prosecutor, Christie would be a credible voice.

Monday night’s private meeting of Clinton and Lynch, the top U.S. law enforcement officer, has been criticized because Hillary Clinton is under federal investigation for using a private email server when she was Democratic President Barack Obama’s secretary of state.

The source said campaign associates made clear Christie was not to be used for this purpose.

“They’re saving him for the general election,” the source said. “They don’t want to overexpose him.”

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 shaking up. His stock may have gone down, however, because he has not hesitated to criticize the candidate at times.

Ernst, a first-term senator and military veteran, could help improve Trump’s standing with women. She tacitly supported rival Marco Rubio during the Republican nominating campaign, though she has promised to support the party’s nominee.

Ernst, who turned 46 on Friday, said earlier this month that the Trump campaign had not contacted her.

The same goes for Oklahoma’s Fallin, who was among several Republican governors who met jointly 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,” Fallin, 61, said in a statement.

Some Republicans could be considered even if they have not had recent contact with the campaign. Alice Stewart, a former spokeswoman for U.S. Senator Ted Cruz’s presidential campaign, said the Texan’s running mate, Carly Fiorina, was only told late in the vetting that she might be picked.

Trump’s vetting is being conducted by Washington lawyer A.B. Culvahouse, a longtime fixture in national Republican politics.