(CNN) - It was the poster child for outside spending the last two elections cycles, but so far in the 2014 midterms, American Crossroads has been relatively quiet.
That apparently ends now.
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The pro-GOP outside group confirms to CNN that it will spend around $10 million to run ads in four crucial U.S. Senate races in Alaska, Arkansas, Colorado and North Carolina. If the Republicans win back those four Democratic held seats plus two more this November, they would regain control of the Senate.
The group, co-founded and steered by Karl Rove, says it will spend more than $3.5 million in North Carolina, where first-term Democratic Sen. Kay Hagan faces a challenging re-election against state House Speaker Thom Tills. The spots will start May 20th and run intermittently through the end of August. Crossroads will shell out more than $2.8 million to run spots from June through August in Colorado, where first-term Democratic Sen. Mark Udall faces a tough GOP challenge from Rep. Cory Gardner.
Crossroads says it will spend more than $1.7 million starting next month in Arkansas, where two-term Democratic Sen. Mark Pyror could face a rough re-election against GOP freshman Rep. Tom Cotton. And in Alaska, where Democratic Sen. Mark Begich will have a fight on his hands as he runs for a second term, the group will shell out $1.8 million to run ads.
A Crossroads official describes the new effort as an "initial" buy. The spending is divided between American Crossroads, the super PAC, and Crossroads GPS, the non-profit 501c4.
Last week the group reserved more than $5 million in ad time in Alaska from September 8 through October 26.
After the January 2010 "Citizens United" Supreme Court ruling that removed legal barriers preventing corporations and unions from spending unlimited sums on federal elections, which opened the flood gates to outside groups, Crossroads became a major player in campaign politics. The group spent around $70 million in the 2010 midterms and $175 million in the 2012 cycle.
But Crossroads went through a dry spell after the 2012 elections, following disappointment by Republicans over President Barack Obama's re-election.
So far this cycle the group has spent around $700,000 in New Hampshire to criticize Democratic incumbent Sen. Jeanne Shaheen (who could also face a challenging re-election) over her support of the health care law. It went up with spots in support of former Alaska Attorney General Dan Sullivan, considered the establishment favorite in that state's GOP Senate primary battle. And it shelled out nearly $2 million in recent weeks to back Tillis in North Carolina, in his Senate primary over a bunch of more conservative rivals.
But that's paled in comparison to what the pro-GOP Americans for Prosperity has spent to run commercials. That group, backed by the deep pockets of the billionaire industrialists David and Charles Koch, has spent more than $35 million so far this cycle. And the top spender among pro-Democratic outside groups, the Senate Majority PAC, has spent more than $11.1 million to run spots.