US election 2012: Rick Santorum endorses Mitt Romney
Failed US Republican presidential candidate Rick Santorum has formally endorsed his former rival Mitt Romney.
In a late-night email , he urged his supporters to back the presumptive nominee in order to deny President Barack Obama a second term.
Mr Santorum said he was impressed by Mr Romney's "deep understanding" of economic and family issues, following a meeting with him last week.
His support may now help Mr Romney win over religious conservatives.
Rick Santorum ended his bid for the White House in April after Mr Romney achieved an unbeatable lead.
"Above all else, we both agree that President Obama must be defeated. The task will not be easy. It will require all hands on deck if our nominee is to be victorious," he said.
"Governor Romney will be that nominee and he has my endorsement and support to win this the most critical election of our lifetime," he added.
Mr Santorum clashed bitterly with Mr Romney during months of competitive primaries and caucuses. At one point, he called Mr Romney the worst Republican in the country to challenge Mr Obama.
But following "candid" discussions in Pittsburgh on Friday, which focused on the family and its "foundational role in America's economic success", Mr Santorum said they had found common ground.
He said they agreed "the need for lower taxes, smaller government, and a reduction in out-of-control spending".
"We certainly agree that abortion is wrong and marriage should be between one man and one woman," he added.
A series of negative campaign ads and videos attacking Mr Romney have now been removed from Mr Santorum's campaign YouTube account .
Last week, former challenger Newt Gingrich formally pulled out of the race and gave Mr Romney a lukewarm endorsement, saying he was a preferable conservative alternative to Mr Obama.
Texas Congressman Ron Paul remains in the race, but has no chance of defeating Mr Romney.