More importantly, Romney urged his 286 delegates to vote for McCain during the party convention this summer in St. Paul, Minn. McCain has 815 delegates, CBS reported; 1,191 delegates are needed for the party nomination.

"In the thick of the fight its easy to lose your opponents' finer qualities," said Romney, who during the campaign called McCain "liberal" and swapped sharp exchanges during debates.

McCain, he said, "capable of leading our country during a dangerous hour."

McCain said Romney's campaign "helped me become a better candidate." He said the former Massachusetts governor would help him "draw the stark differences that exist" between the Republican candidates and the Democratic candidates.

Former Arkansas Gov. Mike Huckabee told CNN he planned to remain in the race "until somebody has 1,191 delegates."

"This election ought to be about choices and voices, not a coronation," Huckabee said.