Mitt Romney is seriously considering another run for the White House and has told one Republican he “almost certainly will” jump into the 2016 race, according to The Washington Post.

Romney, the GOP’s nominee for president in 2012, has been working the phones, talking over the possibility with his former running mate, Rep. Paul RyanPaul Davis RyanYou just can't keep good health policy down Trump blasts Congress for sending him omnibus bill that 'nobody read' Students bash Congress for inaction on gun control MORE (R-Wis.); two 2012 challengers, former Speaker Newt Gingrich (R-Ga.) and former Gov. Tim Pawlenty (R-Minn); and former Sen. Scott Brown (R-Mass.). Republican sources who spoke with The Post said that he's likely to run again. 

A Romney candidacy would upend the 2016 race, and with unpredictable results, as it has been decades since a nominee who lost the presidency tried for a second time. The last losing nominee to run again in consecutive years was Adlai Stevenson, the Democratic nominee in1956 who was then defeated by John F. Kennedy in 1960.

While the former Massachusetts governor would have the benefit of name recognition and presidential experience, convincing the Republican Party to give him another shot at the White House could prove a tough sell.

According to The Post, Romney has told Republicans his third bid for president would be further to the right of former Gov. Jeb Bush, who is mulling a run and appears poised to announce his candidacy in the coming weeks.

Romney has typically been cast as a GOP “establishment” candidate, which could make him a rival not only of Bush, but also 2016 contenders like Gov. Chris Christie (R-N.J.), and Gov. Scott Walker (R-Wis.), who all are flirting with bids.

The talk of a another Romney run exploded on Friday after he told a group of donors he wants to run again, after insisting as recently as October that he had no interest in seeking the nomination again.

Gingrich told the Post that he told Romney that the current GOP field has “runners, but no frontrunners." Judd Gregg, a former New Hampshire Senator and op-ed columnist for The Hill, also confirmed that Romney is “reaching out to people.”

“My sense is he feels strongly he has an opportunity to do what was incomplete last time,” Gregg told the Post.

“He figures there’s a lot of buyer’s remorse now and that his message is a good message and it’ll resonate.”

Romney’s move puts him right back into the conversation as a leading candidate for the GOP nomination. A December McClatchy-Marist poll showed Romney leading all major prospective GOP candidates with Republican-leaning voters, holding a five-percentage point margin over Jeb Bush.

The poll also found that Jeb Bush had the most to gain if Romney ultimately decided to sit out of 2016. Without Romney in the race, Bush becomes the leader, with a four-percentage point margin over former Arkansas Gov. Mike Huckabee.  

Ryan, Romney’s running mate in 2012, told NBC News on Monday that he wouldn’t run for president in 2016 and will instead focus on his new role as House Ways and Means Committee chairman.