A number of high-profile Republican legislators have recently backed Romney, including Sen. Marco RubioMarco Antonio RubioCongress — when considering women’s health, don’t forget about lung cancer Anti-Maduro Venezuelans not unlike anti-Castro Cubans of yore Tax reform postmortem reveals lethal dose of crony capitalism MORE (R-Fla.) and House Budget Committee Chairman Paul RyanPaul Davis RyanStudents arrested protesting gun violence outside Paul Ryan’s office Parkland father calls out Trump, McConnell, Ryan after Santa Fe shooting GOP revolts multiply against retiring Ryan MORE (R-Wis.), the author of a budget proposal that has served as a conservative litmus test. The endorsements are a boon for Romney and a further blow for Rick Santorum, Newt Gingrich and Ron Paul, all of whom are trailing in the number of delegates and endorsements.

On Sunday, Senate Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellTrump's plan to claw back spending hits wall in Congress GOP lawmakers want Trump to stop bashing Congress Parkland father calls out Trump, McConnell, Ryan after Santa Fe shooting MORE (R-Ky.) said that the Republican nominating process was virtually over and that Romney was clearly the GOP's 2012 presidential nominee. McConnell did not, however, endorse Romney.

"I think he’s going to be an excellent candidate and I think the chances are overwhelming that he will be our nominee," McConnell said on CNN's "State of the Union." "It seems to me that we’re in the final phases of wrapping up this nomination and most of the members of the Senate Republican Conference are either supporting him or have the view that it’s time to turn our attention to the fall campaign and begin to make the case against the president of the United States."

In the same interview on Monday, Portman, whose name has come up on some shortlists for the No. 2 spot on the Republican presidential ticket, said he was "not interested" in running for vice president.