Liberals Keep Heat on Moderate Dems

Updated at 4:30 p.m. ET with new information.

Moderate Democrats are sure to come under fire from both the left and the right on health care reform this August, and one particular senator is already feeling the heat.

If the liberal campaign against Sen. Ben Nelson (D-Neb.) is any indication of what this month will be like, the senator said recently, the whole health care reform effort could be upended.

The groups the Progressive Change Campaign Committee (PCCC) and Democracy for America (DFA) launched an ad on Friday, running in Washington, D.C. and Nebraska, featuring a small business owner who says Nelson is "leading the charge to delay health reform this summer." The ad is accompanied by an open letter to Nelson asking for a government-sponsored health insurance option, signed by more than 30,000 people.

Nelson spokesman Jake Thompson fired back, saying in a statement that "if this is an indication of the politics going into August, then health care reform may be dead by the end of August."

"These scare tactics are certain to further divide the public on health care reform, make it less likely Congress will pass real reform and call into question the motives of those who say they want reform, but use the issue to raise money to try to buy influence inside the Beltway," he said.

Adam Green, co-founder of the Progressive Change Campaign Committee, responded that if Nelson stands behind Thompson's statement, he will prove himself "a fundamentally corrupt and out-of-touch politician who feels perfectly comfortable lying to his constituents and going to bat for private insurers who fear competition and want to rip off the people of Nebraska."

PCCC has rallied its supporters with Nelson's comments, raising enough money to triple its ad buy in Nebraska and double it in Washington, the group announced today. The ad will play 600 times in Nebraska, and the group is aiming to raise more funds to increase that number.

"Bold progressives don't cave to intimidation from corporate Democrats," PCCC campaigner Michael Snook wrote in an e-mail to supporters today.

Watch the PCCC/ DFA ad below: