01/04/2012 12:10 am ET Updated Jan 04, 2012

John McCain To Endorse Mitt Romney In 2012 GOP Primary Race

Sen. John McCain (R-Ariz.) will throw his support behind former Massachusetts Gov. Mitt Romney in the race for the Republican presidential nomination.

A former aide to McCain told BuzzFeed that the Arizona Republican will endorse Romney on Wednesday in the key early primary state of New Hampshire.

CNN later confirmed the report.

McCain, who ran as the Republican party's presidential nominee in 2008, signaled to The Hill last month that he would line up behind one of the GOP candidates pursuing the White House, likely sometime after the Iowa caucuses.

Romney proved a valuable champion for McCain during his presidential campaign in 2008 and later, in 2010, during his primary fight against fellow Republican J.D. Hayworth.

The Hill reported last month that McCain had considered Romney an integral part of his White House bid:

"He went wherever and whenever he was asked," said a source familiar with Romney’s contribution to the campaign after the former Massachusetts governor dropped out of contention.

In backing behind Romney, McCain joins a power-packed slate of surrogates that includes popular Republican politicians such as New Jersey Gov. Chris Christie, Sen. John Thune (R-S.D.), Rep. Aaron Schock (R-Ill.) and Rep. Jeff Flake (R-Ariz.).

Romney has not hesitated to use his endorsements to his advantage. As The Huffington Post's Jon Ward reported last month, Romney effectively deployed his heavy-hitters throughout his last-minute campaign tour through Iowa.

Rick Santorum, who emerged Tuesday night as Romney's chief rival, weighed in on the development early Wednesday morning,

The Huffington Post's Sam Stein reports:

Santorum, unwilling to let anyone trample on his night of good news, casually dismissed the significance of John McCain's endorsement of Mitt Romney, which is reportedly coming in New Hampshire on Wednesday.

"It's fine. I expected that," he said. "It's a surprise he hasn't done it earlier."

Appearing on CNN, Santorum went on to laud McCain as a "great man" who had sacrificed more for the country than anyone he knew.

"I commend Governor Romney for getting his endorsement," he added, "but I'm not surprised by it. John is a more moderate member of the Republican team and I think he fits in with Mitt's view of the world."

McCain's reputation for moderation (not entirely supported by his record) makes his endorsement a bit of a double-edged sword for Romney. But not in New Hampshire, where the Arizona Republican remains beloved. If anything, it could persuade Santorum to start framing the next contest as an imbalanced, unreliable affair.

"It would be smart timing," one GOP strategist who has worked with McCain said of the endorsement. "Romney wants to win every day moving into New Hampshire. New Hampshire is probably the only place that a McCain endorsement could really help."