Right after Republicans took control in 2010, House Speaker John Boehner recognized this weak spot and focused a major effort to support the mostly GOP freshmen in these states. Boehner has personally raised more than $10 million to help build local organizations and traveled extensively to stump for these candidates.

Back in April he raised the prospect of potentially significant losses in orphan districts, his remarks intended to warn Republicans focused on the presidential race and the battle for the Senate not to take GOP control of the House for granted.

The battleground for many of these House races has tilted increasingly toward the northeast and Midwest, after so many moderate Democrats lost in southern districts in the 2010 midterms.

In Illinois, Democrats see opportunities to defeat tea party freshman Rep Joe Walsh, seven-term Rep Judy Biggert, and a moderate Republican freshman Rep. Bob Dold.

Democrats have also set their sights on freshmen Reps. Nan Hayworth, Chris Gibson, Ann Marie Buerkle, and Michael Grimm in New York.

Former President Bill Clinton held a rally on Sunday in New York for Sean Patrick Maloney, his former aide who is running against Hayworth. He also recently held an event for five California Democrats, another area where campaign officials argue they can upset several GOP incumbents.

California Rep. Xavier Becerra, one of Pelosi's top lieutenants, told CNN a combination of wins in orphan districts, combined with pickups sprinkled around the country could translate into a path to the majority.

But even Becerra conceded, "we'd need a wind" to get those kind of gains. With a bitterly contested presidential election in 2012 that's expected to be close it's not the political environment for any kind of wave election.

Two years after tea party fuels GOP win, fades as 2010 factor

House Republican candidates are still stressing the core issues that the tea party movement pushed in 2010 -- less government and a focus on cutting federal spending and the deficit, but as one senior GOP strategist working on House races explained, they are "not wearing the tea party label on their sleeves."

Democrats, bolstered by polling that shows that many voters blame the tea party as the reason for gridlock in Washington, continue to try to pin the label on virtually every Republican incumbent and challenger.

House Democrats' campaign chief Rep. Steve Israel, D-New York, argued to reporters last month that the "Tea Party Republican Congress has a 13% approval rating," and maintained Democrats have a chance to regain the majority because "there is a deep sense of buyer's remorse spreading throughout this country."

Even in a solidly blue state like Massachusetts, Democrats are trying to brand Tisei, who already said he would break with his party on taxes, as a tea party Republican.

Democrats say control could hinge on unease over Wisconsin Representative and vice presidential nominee Paul Ryan's Medicare plan.

Pelosi insists that Romney's pick of Ryan as his running mate was the game-changing moment in the battle for the House.

"Mark your calendar, August 11th, the day he was chosen gave a clarification to the issue of Medicare," Pelosi said about Ryan on CNN earlier this month. "This is a person who has been the destroyer of Medicare guarantee," she added.

Democrats had already been highlighting the Ryan Medicare proposal across the country, but they believe that giving it national prominence helped make their case that the dramatic overhaul the House Budget Committee chairman proposed would prove too alarming to voters.

Democrats hold up their win in a special election last May in upstate New York when Democrat Kathy Hochul linked Ryan's proposal to her GOP opponent Jane Corwin and took over what had been a reliably red seat.

But one top GOP strategist told CNN that that upstate New York special election "was the best thing that ever happened to us. It prepared us, it opened us up, and it gave us a year to explain our plan."

Republicans argued it was the Democrats who were gutting Medicare -- by using more than $700 million in reductions for payments to physicians to pay for Obamacare. The GOP candidate Mark Amodei won that election and the strategy has been replicated by candidates ever since.

With the bulk of this cycle's competitive races concentrated in districts represented by the more moderate members of each party, the outcome of this election will mean an even more polarized House in 2013.

The GOP conference will include even more conservatives and the likely loss of more moderate Democrats, whose ranks were already decimated in 2010, will tilt the Democratic caucus further to the left.

A recent study by the Cook Political Report of all congressional districts found that the number of swing districts in the United States went from 164 to 99 in the last 14 years. That decline will undoubtedly have an impact on the ideological divide between the two parties in the House not just this year, but in future elections.

"There's a remarkable reduction in the number of members who have an incentive to compromise," Wasserman told CNN.