Democrats in Congress have repeatedly accused Republican negotiators of being beholden to freshmen and Tea Party conservatives. But the Democrats have problems in their ranks as well. The Democratic left is equally determined to stop President Obama from making concessions they think are wrong, especially on entitlements.

Obama's willingness to include $650 billion in cuts to entitlements such as Medicare in a budget deal that was on the table last week was rejected by his liberal base.

"I think every politician of both parties ought to understand the firestorm that would result with the a backroom deal if you made significant changes in these basic programs," said  Robert Borosage of progressive think tank Campaign for America's Future.

Moveon.org and other liberal groups went even further, leveling political threats at the president, organizing what it called "an emergency campaign to push back."

It urged members to call Obama's reelection headquarters in Chicago and other Democratic campaign organizations to condemn any deal that cut entitlements and did not raise taxes on the rich.

More On This...

"It would be a betrayal of core Democratic values and could have serious consequences for the base's involvement in next year's elections," wrote spokesman David Fenton in describing the campaign from Moveon and several other liberal groups.

The emergency push back campaign also warned that liberal voters are "making tens of thousands of calls right now to Democrats in the House and Senate...." to criticize the President's proposal.

Some Democrats need little encouragement to oppose changes in entitlements. "We do not support cuts in benefits on social security and Medicare," House Minority Leader Nancy Pelosi, D-Calif., said in a statement that mirrors ones she makes nearly every day as negotiations go on.

Liberal groups sharply criticized what they said was  Obama's embrace of an increase in the eligibility age for Medicare and a change in the inflation measure for Medicare and Social Security.

But Obama has repeatedly flirted with the need to make some changes to keep Medicare and other programs from collapsing under the weight of tens of trillions of dollars in unfunded promises. "We should look at what can we do in the out-years, so that over time some of these programs are more sustainable,"  the president said recently.

Borosage argues such programs should be examined in hearings and openly considered, not the subject of closed-door  changes by a few lawmakers. But on Sunday, administration officials defended changes in entitlements as necessary because otherwise they cannot possibly keep all the promises made.

Treasury Secretary Timothy Geithner defends  "entitlement savings to secure Medicare and Medicaid for the future with tax reform that would generate revenues, help us solve this problem."

"This president in all of these negotiations has understood that there must be entitlement reform, and he has been willing to take on his party and some of the so-called sacred cows of the last 25, 30 years, and deal with those issues," said White House Chief of Staff Bill Daley.

But many liberals dispute the need for significant reform and their point seems to have hit home. The debt and deficit plan proposed by Senate Democrats Monday leaves out the cuts to entitlements the president had embraced, just as liberal groups demanded.

But others say there is no way to cut the debt in the future unless lawmakers start trimming the programs that add the most in deficit spending.