- Portman leads by 11 points
- Toomey leads by just 1 point
Marco Rubio of Florida, Richard Burr of North Carolina, Rob Portman of Ohio and Pat Toomey of Pennsylvania all edge out their Democratic challengers by margins ranging from 1 to 11 points, according to a Quinnipiac University survey.
Rubio, who is facing Democratic Rep. Patrick Murphy in November, leads 50% to 43%.
Burr, who is trying to beat back a surprisingly strong challenge from former state legislator Deborah Ross, is winning by 6 points, 49% to 43%.
Portman, an Ohio senator who has opened a wide lead on former Gov. Ted Strickland in recent surveys, is inching out even further ahead -- by 11 points, 51% to 40%, in Quinnipiac's poll.
And Toomey, running against Katie McGinty in one of the country's most expensive races, is ahead by a single point, 46% to 45%.
Republicans were already going to be hard-pressed to hold the Senate given the number of seats they are defending. And Donald Trump's struggles in a number of swing-states -- which double this year as many Senate battlegrounds -- requires some Republicans to run well ahead of their presidential nominee in order to hold their seat in Congress.
Democrats believe they are likely to pick up at least two GOP seats in Illinois and Wisconsin. Other competitive states include Indiana, New Hampshire and the sole Republican pick-up opportunity: Nevada.
Quinnipiac surveyed 601 likely voters in Florida for a margin of error of 4 percentage points; 751 likely voters in North Carolina for a margin of 3.6 points; 775 likely voters in Ohio for a margin of 3.5 points; and 778 likely voters in Pennsylvania for a margin also of 3.5 points. The Florida poll was conducted August 31-September 7. The three other polls were conducted August 29-September 7