Mitt Romney is endorsing former rival John McCain as the 2008 Republican presidential nominee faces a fight to keep his Senate seat.
Romney said in a statement Tuesday that the Arizona senator's "record of service and sacrifice for America is honored by all."
The former Massachusetts governor adds that it's "hard to imagine the U.S. Senate without John McCain."
McCain is facing a Republican primary challenge from former House member J.D. Hayworth.
McCain and Romney clashed bitterly at time in the 2008 race for the GOP nomination. After McCain pulled ahead, Romney not only endorsed him but energetically campaigned for him.
McCain's former running mate, Sarah Palin, is also backing him. She and Romney are potential rivals in the 2012 presidential race.
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