[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/images/12/14/art.lieberman.jpg caption="Senate Democrat fuming at Lieberman."]
Washington (CNN) - Senate Democrats struggled to find a way forward on health care legislation Monday in the wake of Sen. Joe Lieberman's announcement that he will oppose a leading compromise proposal Democrats saw as their best way to get the 60 votes needed to pass a bill.
Privately fuming at the Connecticut senator, Democrats wrestled with whether to meet his demand to remove an expansion of Medicare from the bill - a move that would anger liberal Democrats who believe they've already made concessions on a government insurance option.
Democrats "may have to do what Mr. Lieberman wants," liberal Sen. Tom Harkin of Iowa said to CNN.
Democratic leaders, who had hoped to file procedural motions this week to end debate and begin voting on the bill, called a special caucus meeting for 5:30 pm Monday to assess their bleak situation.
"It's hit a rough spot," acknowledged a Democratic leadership aide who said there is a "decent level of concern" about the fate of the compromise bill.
Asked if Senate leaders are scrambling to find a "Plan C" - something that could attract Lieberman without losing liberals - the aide said they are "working on it."