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To be clear, Republicans hold advantages in Senate races where the presidential campaign is not as much of a major factor: Indiana, Nebraska and North Dakota. But victories in battleground states would offset any GOP losses in Maine and Massachusetts and could mean the difference between the majority and minority in the Senate.
It's a different story in the House. Republicans controlled the redistricting process in most key states last year, solidifying large gains they made in 2010. As a result, House candidates are not as vulnerable to Romney's potentially disappearing coattails.
"I think that it is possible there is a big cement truck that's just unloaded on downballot races," said Brad Todd, a veteran Republican consultant. "I think we may be seeing the Congressional races hardening much earlier than we ever have before. I'm seeing far less undecided in Congressional races than I ever have in September."
House Democrats pounded away at Republicans for Romney's comments this week. The Democratic Congressional Campaign Committee fundraised off of Romney's political woes, warning potential donors that super PACs would transfer presidential race resources to the House.
House Republicans kept silent for the most part, waiting out the media firestorm.
"Everybody has to run their own campaign," said businessman Jason Plummer, a Republican nominee locked in a tough race for retiring Rep. Jerry Costello's (D-Ill.) seat, on a Wednesday conference call with reporters. "We're running a very aggressive race based on jobs."
On the flip side, House Democrats have dealt with a downballot back draft for months in some districts. Republican redraws forced Democrats such as Reps. Mark Critz (Pa.), Mike McIntyre (N.C.) and John Barrow (Ga.) to seek re-election in conservative districts. As a result, the trio has been running against the Obama administration since before the ink dried on the maps of their new districts.
Most projections show House Republicans on track to keep their majority in the next Congress. Redistricting shrunk the playing field to a few dozen seats. It's a change from the past three volatile cycles in Congress, when as many as 100 seats were in play.
But history shows it's more common for Congress to experience minimal change in a cycle when the president is up for re-election. In 2004, Republicans picked up a net of four Senate seats and three House seats. In 1996, Republicans picked up two Senate seats but lost nine House seats. In 1992, Republicans picked up 10 House seats and broke even in the Senate.
"Coattails generally happen [in a] regime-change election, when you're switching from one party to the other, not when presidents are re-elected," said former Rep. Tom Davis (Va.), an ex-National Republican Congressional Committee chairman.
Steven T. Dennis contributed to this report.