WASHINGTON – Senate Democrats on Tuesday posed an ultimatum to Speaker John Boehner (R-OH) on the budget: Bring your tea party "extremists" in line or prepare for a government shutdown come April 8.

On a conference call with reporters, Sens. Barbara Boxer (D-CA), Richard Blumenthal (D-CT), Thomas Carper (D-DE) and Ben Cardin (D-MD) took turns excoriating Boehner for what they depicted as the House GOP leadership's capitulation to the 87 House freshmen threatening to scuttle any deal with insufficiently high spending cuts.

"Our problem is that we see now that Speaker Boehner is yielding to the extremes of his party, basically saying he's not going to negotiate, take it or leave it," Cardin said, insisting that Democrats were eager to compromise and cede ground to reach a deal.

"The anchor around the neck of these negotiations is a relatively small, extreme group of ideologues on the Republican side," Blumenthal added. "They are an anchor that needs to be cut loose. Only Speaker Boehner can do it, and he needs to do it now, otherwise we will have a shutdown. The ball is in his court."

House Republicans want the budget to reflect the $61 billion in spending cuts they approved last month. That's a non-starter for Senate Democrats, who want the cuts to total roughly $20 billion and have been trying to persuade Speaker John Boehner (R-OH) to bring his figure down. Leaders of both parties have shown flexibility on the substance, but by compromising, Boehner would risk alienating his 87 tea party freshmen and possibly inciting a GOP revolt.

"There's not enough skin in the game by those who are talking about a shutdown," Boxer said, accusing tea party House members of demanding painful cuts while showing little or no flexibility in the negotiations.

Boehner shot back at the Senate Democrats, arguing Tuesday that the House measure must be the starting point for negotiations because the Senate has not passed a budget.

"The American people want us to cut spending and keep the government open, and the House has passed legislation to do that," Boehner spokesman Michael Steel told Raw Story in an e-mail. "The Senate has failed to act, or even offer a plan. If the Democrats who run Washington want to point fingers, they ought to buy a mirror."

The Democrats also fretted that the "riders" Republicans insist on -- the provisions imposing restrictions on federal agencies such as the EPA and curbing grants to Planned Parenthood -- have nothing to do with the budget are are ideological pet-projects that should be debated separately.

"I think Republicans lose a lot of credibility of they hold off an agreement based on riders," Carper said.

A GOP aide told Raw Story that the riders are fair game. "Policy restrictions are a routine part of the Appropriations process," the aide said, "and I'm certain the senators on that call have voted for hundreds – if not thousands – of them in the past. Their position is simply not credible."

Signs of a deal appeared increasingly unlikely Monday as leaders of both parties angrily blamed each other for the broken down negotiations, which stalled last week.