This is the second burst of ads from the group targeting Democrats in Missouri, Massachusetts, Montana and Nebraska, hitting airwaves one month after an initial round where Crossroads spent almost $2 million in those states and another $2.6 million to attack Democrats in five swing states.

The ads, which will air for two weeks, lambaste Democrats for spending recklessly and allowing the national debt to escalate, and work to tie the candidates to an unpopular President Obama.

“Look at the damage he did: higher taxes, cutting Medicare spending, embarrasing Nebraska. Ben Nelson sold out to Obama when it counted most," says one of the ads.

Crossroads will spend almost $123,000 attacking Sen. Ben Nelson (D-Neb.), who hasn’t yet announced whether he will seek reelection. Another $251,000 will go to ads targeting Sen. Claire McCaskillClaire Conner McCaskillTrump urges anti-abortion advocates to rally in November Calif. gov candidates battle for second place Senate panel advances Trump's CIA nominee MORE (D-Mo.) by portraying her and Obama as one and the same. In Montana, the group will spend $136,000 hitting Sen. Jon TesterJonathan (Jon) TesterTrump urges anti-abortion advocates to rally in November Overnight Finance: House sends Dodd-Frank rollbacks to Trump | What's in the bill | Trump says there is 'no deal' to help ZTE | Panel approves bill to toughen foreign investment reviews House votes to ease regulation of banks, sending bill to Trump MORE (D).

But the biggest buy is saved for Massachusetts, where Crossroads has made Democrat Elizabeth WarrenElizabeth Ann WarrenRising star Abrams advances in Georgia governor race Progressive rise is good news for Sanders, Warren Juan Williams: Trump gives life to the left MORE a top target of its 2012 election efforts. The group will spend $524,000 to undercut Warren in December.

“Tell Professor Warren: We need jobs, not more bailouts and bigger government,” the Massachusetts ad says.

The behemoth of outside spending for the 2012 cycle, Crossroads GPS, together with its affiliate, American Crossroads, has already dropped more than $20 million attacking Democrats and Obama this year.

From both sides of the political divide, outside groups have unleashed more than $35 million to influence election results, according to a recent investigation by The Hill.

Watch the ads: