So far in 2012, Democratic groups have generally been able to keep pace with the competition. Outside groups have spent about $60 million trying to help GOP candidates since June 1 and about $49 million trying to help out Democratic candidates, according the Sunlight Foundation.
But some of the Republican support groups are just getting started. Beginning Saturday, Crossroads GPS, one of the deep-pocketed groups co-founded by Karl Rove, is launching a three-week, $8.1 million broadcast campaign in 11 House districts in New York to Michigan, Iowa, Illinois, Nevada, Indiana and California, according to Nate Hodson, the group's spokesman.
The Chamber of Commerce launched an $8 million ad campaign last week on behalf of 20 GOP candidates in close House races in California, New York and Illinois. It also weighed in for two Democratic incumbents. Until then, the chamber had focused most of its spending on Senate races.
American Action Network and the Congressional Leadership Fund, two Republican support groups led by former Sen. Norm Coleman, have spent about $3.1 million so far on House races. This week they said they will spend at least $13.5 million more during the campaign's final month.
After focusing on the presidential and Senate races the past four months, Crossroads groups also are beginning to pour more resources into House races to assist Republican candidates.
Crossroads GPS dumped $716,000 in New York in late September for ads aimed at defeating Democratic Rep. Tim Bishop and re-electing Republican Rep. Chris Gibson. A spokesman said this week the groups were planning to spend tens of millions of dollars more over the next four weeks to "protect the majority in the U.S. House and promote a conservative agenda."
A Democratic official who tracks media buys said Thursday that Crossroads GPS has purchased nearly $7 million worth of broadcast and cable ads to run later this month in eight House races.
Americans for Tax Reform has purchased nearly $6 million in broadcast and cable ads in six House races, the official said on condition of anonymity. The group, led by Grover Norquist, had invested only $500,000 on one House race, in Pennsylvania's 12th Congressional District with the aim of defeating Rep. Mark Critz. Americans for Tax Reform presses lawmakers to sign a pledge promising not to increase income taxes. The organization did not return calls seeking comment.
Dan Conston, a spokesman for the American Action Network and Congressional Leadership Fund, said the late surge in spending by the Coleman groups is by design because many voters don't pay attention to political ads until late in the campaign.
"With a political environment this competitive, we're pleased at having spent some resources early but having the lion's share for the final weeks when hard-to-reach undecided voters tune in," Conston said.
Democratic officials say they're not surprised by the recent ad buys and announcements. They've been bracing for a late surge in outside spending after it proved so effective in helping the GOP win control of the House in 2010, when 87 GOP freshmen were elected.
"We've been expecting this all along," said Andy Stone, spokesman for the House Majority Pac, the leading Democratic super PAC in this year's races.
Stone said that the House Majority PAC prepared for the finals weeks by reserving about $20 million worth of television ad time in keys races early in the summer, locking in lower rates than those offered to current buyers.
"As a result, we're getting a better rate, a better deal than the Republicans are," Stone said.
Still, it remains an uphill task for Democrats to win back a net 25 seats to regain control of the House.
Stone pointed to California's 7th Congressional District as an example of how Democratic groups are better prepared to deal with a late surge in outside spending. The race features a rematch between Republican Rep. Dan Lungren and Democratic candidate Ami Bera.
In 2010, American Crossroads spent $682,000 on ads opposing Bera during the final two weeks of the campaign. That represented more than 80 percent of the outside spending that occurred in the entire race. Bera's momentum grounded to a halt after American Crossroads intervened.
"He was surging in the polls and becoming a very serious contender. The polls were going up and up and up," said Bera's current campaign spokeswoman, Allison Teixeira. "Then, big money came in from Karl Rove's super PAC and started airing all kinds of negative ads. It was still a tight race, but he (Bera) lost his momentum from that."
In the end, Lungren won by a margin of 50.1 percent to 43.2 percent. Outside groups have already spent more than $5 million on the race this year. Democratic-aligned groups have more than matched the nearly $500,000 the Chamber of Commerce has spent opposing Bera. The House Majority PAC has spent nearly $400,000 on ads opposing Lungren and the Service Employees International Union PAC spent a like amount. The American Federation of State, County and Municipal Employees also spent $800,000 opposing Lungren in the final week of September.
National Democrats made two tactical decisions to minimize the impact of a late surge in outside spending from GOP groups. They decided to purchase air time early in the race and also placed more emphasis on raising money directly for House candidates rather than Democratic Congressional Campaign Committee itself.
Democratic officials explained that in some TV markets, candidates pay only one-third the rate that third-party groups are charged for ad time.
National Republicans said the outside money is welcome because it will help counter spending by labor unions.
"Labor has always been this shadow army for Democrats in elections and a lot of the money they spend on the ground and in mail and TV is not as noticed as a lot of outside groups, but it certainly makes an impact," said Paul Lindsay, communications director for the National Republican Congressional Committee.
The outside spending for House races has been heaviest in the Democratic strongholds of California, $24.3 million; Illinois, $15.5 million; and New York, $15.4 million, according to the Sunlight Foundation.
Overall, outside spending for House races is expected to at least double what took place in the 2010 elections. Then, outside groups spent nearly $94 million on House races. This cycle, outside groups have already spent $151.5 million, according to the Center for Responsive Politics.