Republican stalwarts Newt Gingrich and Chris Christie are at the top of Donald Trump's short list to be his vice presidential running mate, sources say, but the real estate developer is casting a wide net that also includes Indiana Governor Mike Pence.
With less than three weeks to go until he is formally nominated at the Republican National Convention as the party's candidate in the November 8 election, Mr Trump's search for a number two has intensified.
The wealthy businessman, a neophyte as a politician, has said he wants a seasoned political veteran to help him navigate the power corridors of Washington.
Mr Gingrich and Mr Christie, both loyal to Mr 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 Pence, Senator Bob Corker of Tennessee, Senator Joni Ernst of Iowa and Oklahoma Governor Mary Fallin, Republicans close to the campaign said this week.
"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 Governor Pence," Trump spokesman Jason Miller said in an email.
Mr 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 Mr Trump to adopt a more presidential demeanor.
But since Mr Trump is 70 and Mr Gingrich is 73, they could face difficulty in appealing to a younger generation.
Mr Christie quickly endorsed Mr Trump after dropping out of the race early this year.
A source said the 53-year-old New Jersey governor has emerged as a key adviser to Mr Trump and his campaign team at Trump Tower.
Mr Corker, 63, offers Mr Trump deep foreign policy experience as chairman of the Senate Foreign Relations Committee and, like Mr Trump, believes the Republican Party needs to be shaken up.
Ms Ernst, a first-term senator and military veteran, could help improve his standing with women voters.
But she was a tacit supporter of rival Marco Rubio during the Republican nominating campaign.
Ernst, who turned 46 on Friday, said earlier this month she had not been contacted by the Mr Trump campaign.
The same goes for Oklahoma's Ms Fallin, who was among several Republican governors at a joint meeting with Mr Trump in June.