Mark Barabak

After Tuesday's victory in winner-take-all Arizona, Trump has 739 delegates, far more than either of his two remaining GOP rivals, Ted Cruz and John Kasich, and more than half the number needed to lock down the nomination.

The target on Sen. Marco Rubio's back grew larger Saturday, as rival candidates, starting with New Jersey Gov. Chris Christie, sought to turn the Florida senator's polish into a liability in a critical debate.

Mitt Romney, calling for a ban on earmarks in Wednesday's GOP debate, pounced on opponent Rick Santorum's record in Congress. "While I was fighting to save the Olympics, you were fighting to save the 'bridge to nowhere,' " he said, referring to the proposed crossing to a Southeast Alaska island that became a symbol of government profligacy.

Standing face-to-face, Mitt Romney and Newt Gingrich traded barbs over honesty and integrity in an acrimonious debate that opened a fierce fight ahead of Florida's crucial presidential primary.