TAMPA, Fla. -- With 24 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.

Early returns show Romney with 49 percent and 30 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.