Republican nominee Mitt Romney’s turbulent few weeks underscore a new reality for embattled Congressional Republicans: They might be on their own in November.

The presidential race is far from over; fewer than 50 days remain before the election, and Democrats and Republicans still expect a competitive race. But as polls show President Barack Obama’s lead strengthening in key states, GOP campaigns cannot count on a strong Romney performance to put them over the top. Republicans seeking re-election increasingly view their races in a vacuum, or at least they hope that’s the case.

“I just don’t think that any of our Members are tied to Romney at all,” said a top House GOP aide who requested anonymity to speak freely. “They just don’t connect the person to Romney, and that’s good for us.”

The stakes are especially high in the Senate, where Republicans must win a net of four seats to take control of the chamber if Obama wins re-election. But a trio of recent polls in three battleground states show Senate candidates often tied with Romney – and trailing Democratic opponents.

In Ohio, Sen. Sherrod Brown (D) led state Treasurer Josh Mandel (R) by  7 points in an NBC News/Marist poll out last week. That survey showed Obama holding the same margin over Romney in the Buckeye State.

Sen. Rob Portman (R-Ohio) cited Mandel’s own polling when asked how Romney’s standing would affect the race.

“Josh’s numbers are better,” Portman said, citing improvement since the start of the race. “He’s gone from 20 points down, to 10 points down, to 5 points down, to some polls showing him in a dead heat.”

But in competitive Virginia, former Gov. Tim Kaine (D) led former Sen. George Allen (R) by 8 points in a Washington Post poll released Wednesday. Obama led Romney by that same margin in the survey.

In Wisconsin, Rep. Tammy Baldwin (D) and  former Gov. Tommy Thompson (R) were tied in a CBS News/Quinnipiac University poll released Wednesday. Obama led Romney by 6 points in that survey.

“If it’s a close election, that means we can do what we need to do,” one top Senate Republican aide said. “If it’s not a close election, that obviously won’t be helpful.”

Even in Massachusetts, where Sen. Scott Brown (R) faces a tough re-election bid against Harvard professor Elizabeth Warren (D), the presidential race is a factor. Brown was one of the first Republicans to distance himself from Romney’s recently revealed comments from a fundraiser.

“We’re two different people, obviously, and people recognize that,” Brown said  Wednesday. “I know she’d like to run against Mitt Romney, but she’s running against me.”

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.