Sen. John McCain has endorsed Mitt Romney in the race for the Republican presidential nomination.

The Arizona Republican, appearing with the former Massachusetts governor at a town hall campaign event in Manchester, N.H., this afternoon, threw his support behind his one-time rival for the 2008 nomination, which McCain won. Romney endorsed McCain in that race after he exited the contest.

“I am really here for one reason and one reason only, and that is to make sure that we make Mitt Romney the next president of the United States of America,” McCain said in an animated stump speech. “And New Hampshire is a state that will catapult him onto victory in a very short period of time.”

Arguing that President Barack Obama has made the country weaker on the world stage, McCain said, “No one will ever say that Mitt Romney will lead from behind.”

The value of an endorsement in the presidential race by a Member of Congress is questionable, particularly at a time when the body has such low job approval ratings with voters.

But McCain has long had a good relationship with New Hampshire voters, winning the Granite State’s first-in-the-nation GOP primary twice — in 2000 and 2008 — and his backing of Romney could help him maintain his strong lead in the state in the runup to the primary vote Tuesday.

Meanwhile, McCain’s endorsement of Romney continues a pattern of GOP establishment figures coalescing around the former Massachusetts governor, who bested former Pennsylvania Sen. Rick Santorum by eight votes in Tuesday’s Iowa caucuses. Sen. Kelly Ayotte (R-N.H.) also has endorsed Romney.

Romney has garnered far more Member endorsements — 61 — than any of his competitors for the 2012 nomination. Santorum, who served in Congress from 1994 to 2006, has received none.

In addition to today’s town hall at Manchester Central High School, McCain was scheduled to join Romney for a similar event at 5 p.m. in Peterborough, N.H.