Incumbent Republican senators in Florida, Ohio, and Pennsylvania all hold leads in their re-election bids, according to polling released Thursday.

Sens. Marco Rubio of Florida and Pat Toomey of Pennsylvania both have double-digit leads, while Sen. Rob Portman of Ohio holds a 7-point edge over Democrat Ted Strickland, according to the Quinnipiac University polling.

Mr. Rubio, who still faces a primary challenger in businessman Carlos Beruff, led Democratic Rep. Patrick Murphy by a 13-point, 50 percent to 37 percent margin. Mr. Rubio also led Rep. Alan Grayson by a 12-point, 50 percent to 38 percent margin.

"The numbers seem to be breaking the Republican way in the battle for control of the U.S. Senate, at least when it comes to the critical swing states of Florida, Ohio and Pennsylvania," said Peter A. Brown, assistant director of the Quinnipiac University Poll.

"Democrats made fun of Sen. Marco Rubio when he opted for a last-minute re-election bid in Florida, but he may be on the way to a last laugh, having quickly opened double-digit leads over both Democratic challengers," Mr. Brown said.

In Ohio, meanwhile, Mr. Portman held a 7-point, 47 percent to 40 percent lead over Mr. Strickland.

And in Pennsylvania, GOP Sen. Pat Toomey held a 10-point, 49 percent to 39 percent lead over Democrat Katie McGinty.

The incumbent senators ran ahead of presumptive GOP presidential nominee Donald Trump in all three states.

In head-to-head matchups with likely Democratic nominee Hillary Clinton, Mr. Trump led by 3 points in Florida, 42 percent to 39 percent, he led by 2 points in Pennsylvania, 43 percent to 41 percent, and he and Mrs. Clinton were tied at 41 percent apiece in Ohio.

"Many talking heads have suggested that with Donald Trump at the top of the GOP ticket, Republican Senate candidates might suffer," Mr. Brown said. "But at least in these three key states, the Republican Senate candidates are running ahead of Trump and don't seem to be hurt by their shared party label."

Florida, Ohio and Pennsylvania are three states Democrats are targeting in their bid to retake control of the Senate, where Republicans hold an effective 54-46 majority.

Alan Grayson

GOP senators lead in Florida, Ohio, Pa.: Poll