GOP Sen. Rob Portman of Ohio leads by 9 points in his re-election bid, while GOP Sen. Marco Rubio of Florida has a smaller advantage, and Republican Sen. Pat Toomey of Pennsylvania is slightly behind, according to polling released Thursday.
Mr. Portman had a 9-point, 49 percent to 40 percent, lead over Democrat Ted Strickland in Ohio, according to the Quinnipiac University poll.
Mr. Rubio, meanwhile, had a 3-point, 48 percent percent to 45 percent, lead over Democratic Rep. Patrick Murphy and a 6-point, 49 percent to 43 percent, lead over Democratic Rep. Alan Grayson in Florida.
In Pennsylvania, Democrat Katie McGinty had a 3-point, 47 percent to 44 percent, lead over Mr. Toomey in the poll.
“At this stage of the campaign, Republican U.S. Senate candidates may be running against their own presidential nominee, Donald Trump, as much as they are against their Democratic opponents,” said Peter A. Brown, assistant director of the Quinnipiac University Poll.
All three Republican incumbents were running ahead of Mr. Trump in the polls. Hillary Clinton led Mr. Trump by 4 points in Ohio, 49 percent to 45 percent, by 1 point in Florida, 46 percent to 45 percent, and by 10 points in Pennsylvania, 52 percent to 42 percent.
“In each of the three key swing states, the incumbent U.S. senators seeking re-election are running better than Trump,” Mr. Brown said. “But if Trump continues to lag behind in the presidential race, that will make it more difficult for GOP candidates, logic holds, up and down the ballot.”
Many polls taken before the Republican and Democratic conventions last month had shown GOP incumbent senators leading their races in such battleground states even when Mr. Trump was behind Mrs. Clinton.
But other surveys taken after the Democratic National Convention have shown that while the senators are still running ahead of Mr. Trump, some incumbents might not escape the fallout if he falls too far behind.
In a head-to-head match-up, Mrs. Clinton led Mr. Trump by 15 points, 52 percent to 37 percent, among likely voters in Wisconsin, according to a Marquette University Law School poll released Wednesday. In the state’s U.S. Senate race, Democrat Russ Feingold led GOP Sen. Ron Johnson by 11 points, 53 percent to 42 percent, among likely voters.
And a Vox Populi Polling survey released Wednesday showed Mrs. Clinton with a 10-point, 41 percent to 31 percent lead on Mr. Trump in New Hampshire, with Libertarian Party nominee Gary Johnson at 11 percent and Green Party nominee Jill Stein at 3 percent.
In the state’s U.S. Senate contest, Democratic Gov. Maggie Hassan held a 3-point, 46 percent to 43 percent, lead over GOP Sen. Kelly Ayotte.
• David Sherfinski can be reached at dsherfinski@washingtontimes.com.
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