Crossroads GPS is beginning today a two-week run of tough ads against Democrats in five of the hottest 2012 Senate races.

The $1.8 million ad buy goes after Senate hopefuls Tim Kaine (Va.) and Elizabeth Warren (Mass.) and incumbent Sens. Claire McCaskill (Mo.), Ben Nelson (Neb.) and Jon Tester (Mont.).

Three of the five ads seek to tie the subject to President Barack Obama and his policies.

Obama is also the subject of new ads from the GOP group the American Action Network. The nearly identical ads slam Democratic incumbents Rep. Larry Kissell (N.C.) and Rep. Leonard Boswell (Iowa).

The ads show images of economically distressed families as a narrator says, “These families try and live within their means.” It then jumps to a shot of the Democratic incumbent with an image of Obama in the background. “But not in Washington, where out-of-control spending puts our economy at grave risk.”

The Crossroads ad airing in Missouri shows images of McCaskill with Obama. It attacks her for the stimulus and the auto and bank bailouts, and to further tie her to the president, it uses the plural pronouns “they” and “them.”

In Montana, GPS is accusing Tester of putting Washington and Obama’s policies ahead of Montana interests. The ad cites as evidence a vote Tester cast that allowed “Obama’s EPA” to regulate dirt. It goes on to describe the move as “big government regulations that could hurt our farmers and jobs.”

Kaine is not an incumbent Senator, but he might as well be in the Virginia GPS ad. As the former Democratic National Committee chairman, he made television appearances promoting the stimulus. The ad features some of those video and print quotes and then describes him as Obama’s “partisan cheerleader.”

The Massachusetts ad seeks to portray Warren as a professor inspiring destruction at Occupy Wall Street.

Another ad in Nebraska has yet to be released but will be begin airing Friday.