Former Massachusetts governor Mitt Romney ended his campaign for the Republican presidential nomination on Thursday, endorsing rival Sen. John McCain, saying it was in the best interest of his party and the nation to do so.

The decision, which he announced at the Conservative Political Action Conference in Washington, comes after Super Tuesday where voters in several states gave Arizona Sen. McCain a sizable lead over the two leading candidates, Romney and former Arkansas Governor Mike Huckabee.

In the race for party delegates, McCain led with 707, to 294 for Romney and 195 for Huckabee. The party requires 1,191 to earn the nomination.

If I fight on in my campaign, all the way to the convention, I would forestall the launch of a national campaign and make it more likely that Senator Clinton or Obama would win, referring to the contenders for the Democratic party's nomination.

He mentioned the delegates lead as a factor in his decision. He also said that despite many differences he agreed with McCain on his stance against terrorism as the U.S. fights a war in Afghanistan and Iraq.

And in this time of war, I simply cannot let my campaign, be a part of aiding a surrender to terror.