Crossroads GPS, the shadowy conservative organization which former Bush White House aide Karl Rove helped found, has launched $1.8 million in advertising attacking five Democratic Senate candidates, including Elizabeth Warren in Massachusetts, according to the arm of the Democratic Party tasked with electing Democrats to the Senate.

The attacks come a full year ahead of the 2012 elections, in which Democrats will be defending their small Senate majority against a Republican onslaught.

Crossroads GPS, which spent heavily on attack ads in the 2010 midterm elections which helped defeat Democrats nationwide, is buying advertising against Democrats in Virginia, Montana, Missouri, Nebraska, in addition to Warren.

“Why Warren? Because she is a true fighter against corporate power and is a serious threat to beat Scott Brown and take back that seat in Massachusetts,” says Guy Cecil, executive director of the Democratic Senatorial Campaign Committee (DSCC).

A former adviser to the Obama administration, Warren has become the frontrunner for the 2012 Democratic nomination for Senate from Massachusetts by running a feisty, populist campaign.

She would oppose Brown, the Republican who won an upset victory in 2010 to fill the unexpired term of the late Democratic Sen. Ted Kennedy. Brown now seeks his first full, six-year term.

The Crossroads ad against Warren attacks her for her support for the ongoing Occupy Wall Street protests against corporate influence on government.

YOU CAN WATCH VIDEO OF THE CROSSROADS ATTACK AD AGAINST WARREN HERE:

Click here to view the embedded video.

Senate Democrats face a challenging political environment next year. They must defend 23 seats — more than twice as many as their GOP counterparts. A net loss of just four seats would throw the Senate majority back to the Republicans.

In an email Friday, the DSCC sought to raise $50,000 by midnight for what Cecil calls its “Year Out Project.”

“Every dollar we fall short is a dollar Karl Rove can spend attacking our candidates without challenge,” he says. “With 23 seats to defend, we can’t afford that. We would lose the Senate, and the new leadership would have Rove on speed dial.”

Scott Nance is the editor and publisher of the news site The Washington Current. He has covered Congress and the federal government for more than a decade.