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 McCaskillDemocrats turn on Al Franken Trump rips Dems a day ahead of key White House meeting The Hill's 12:30 Report 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) TesterGOP and Dems bitterly divided by immigration Senate panel moves forward with bill to roll back Dodd-Frank GOP defeats Schumer bid to delay tax vote MORE (D).

But the biggest buy is saved for Massachusetts, where Crossroads has made Democrat Elizabeth WarrenElizabeth Ann WarrenOvernight Regulation: Net neutrality supporters predict tough court battle | Watchdog to investigate EPA chief's meeting with industry group | Ex-Volkswagen exec gets 7 years for emissions cheating Overnight Tech: Net neutrality supporters predict tough court fight | Warren backs bid to block AT&T, Time Warner merger | NC county refuses to pay ransom to hackers Avalanche of Democratic senators say Franken should resign 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: