TAMPA, Fla. (AP) - With 38 percent of the precincts counted, Mitt Romney has jumped to a commanding lead in Florida's Republican presidential primary, the biggest test so far in an increasingly negative race against Newt Gingrich.

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Early returns show Romney with 48 percent and 31 percent for Gingrich.

The winner-take-all primary is worth 50 Republican National Convention delegates.

About half of Florida primary voters say the most important factor for them is backing a candidate who can defeat President Barack Obama in November. That's according to early exit poll results conducted for The Associated Press and television networks.