Incumbent Republicans Pat Toomey and Marco Rubio are struggling to hold on to their seats in their respective Senate races, according to new poll out Thursday -- and it could be due to a "Trump effect."
The Quinnipiac University survey shows Sen. Marco Rubio of Florida in a too-close-to-call race with 48 percent of support against Democratic Rep. Patrick Murphy, who is at 45 percent. That's within the Florida poll's margin of error of three percentage points. Rubio has a larger advantage against another Democrat in the race, Florida Rep. Alan Grayson, 49 to 43 percent.
In Pennsylvania, Sen. Pat Toomey lags behind his Democratic challenger Katie McGinty by three points, 44 percent to 47 percent. This race too is within the poll's margin of error of 3.4 percentage points.
There's good news, however, for GOP Sen. Rob Portman in Ohio, who faces off against Democrat and former Gov. Ted Strickland. Portman leads Strickland with a comfortable nine-point margin: 49 percent to the Democrat's 40 percent.
Peter Brown, assistant director of the Quinnipiac University poll, is attributing the softening support for incumbent Republicans to Donald Trump at the top of the general election ticket.
"In each of the three key swing states, the incumbent U.S. senators seeking re-election are running better than Trump," 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."
The latest Quinnipiac University presidential surveys show Clinton leading Trump in Florida (46 percent to 45 percent), in Ohio (49 percent to 45 percent) and in Pennsylvania (52 percent to 42 percent).
The Quinnipiac polls were conducted July 30-August 7. In Florida, the university surveyed 1,056 voters with a margin of error of three percentage points. In Ohio, they polled 812 voters with a margin of error of 3.4 percentage points. In Pennsylvania, they surveyed 815 voters with a margin of error of 3.4 percentage points.