As prospects for Congress’ special deficit reduction supercommittee to reach an agreement have dimmed, a bipartisan group of lawmakers from both chambers joined Wednesday to urge the group to “go big,”and strike a deal to cut as much as $4 trillion from the nation’s borrowing over the next 10 years.

The group included several dozen of the 45 Senators and 100 Representatives who had signed separate letters pushing the group to consider both raising revenues and cutting entitlements to reach a deal, prospects that would anger loyalists in both parties.

But the event represented a rare bicameral effort and members of the coalition included members from across ideological spectrums.

They said their goal was to tell the supercommittee that support exists among rank-and-file members for a deal that would make a significant dent in the nation’s debt trajectory and that failing to do so could shake world markets and further erode public confidence in Congress.

“This debt and deficit debate has become like a proxy for whether our democratic institutions are up to the job in the 21st century,” said Sen. Mark Warner (D-Va.), an organizer of the effort.

Among the attendees was Sen. Lamar Alexander (Tenn.), the Senate's 3rd ranking Republican, who notably urged supercommittee members to include more tax revenue—long a sticking point for the GOP—in their offer. Noting that committee members already have included some revenues and Democrats have offered some difficult entitlement cuts, he urged both sides to now concede more. "Both need to put more on the table and get a result, and we're here to support them," he said. 

The message of encouragement comes as chances of the 12-member supercommittee to reach a deal to cut at least $1.2 trillion from deficits by a Nov. 23 deadline appear especially bleak.

Republican supercommittee chairman Jeb Hensarling (R-Tex.) said in a television interview Tuesday evening that GOP negotiators had gone as far as they could in including higher revenues in a week-old offer to overhaul the tax code in a way that would produce $300 billion in new revenues. That plan had been rejected by Democrats because the GOP tax overhaul would also cut tax rates for the wealthy.

Hensarling's comments came despite weekend talks about a deal that would include as much $650 billion in new tax revenue over the next decade, $100 billion of which would come immediately through higher taxes on some businesses and an additional $550 billion to be found later through a full overhaul of the tax code that would cap deductions but lower tax rates.

In response, panel member Rep. Chris Van Hollen (D-Md.) said it appeared Republicans were “throwing in the towel” on the talks.

The “go big” group offered no specifics about the details of a package they could support, but promised to be open-minded if the supercommittee could make a deal. Any agreement reached by the panel would get fast-track consideration by the rest of Congress.

But if Congress failed to approve the group’s recommendations by Dec. 23, federal budgets would automatically be cut by a total of $1.2 trillion over the next decade, split evenly between domestic and defense programs.

“I’m very happy to stand here with these people today and say, supercommittee, ‘we’ve got your back,’” said Sen. Saxby Chambliss (R-Ga.). “‘We support you. We look forward to working with you on whatever course you decide to take to make sure we do the right thing for the American people.’”

Included in the group were members of the Senate’s so-called Gang of Six, which this summer outlined its own framework to cut deficits by $3.7 trillion.

But the group has not circulated the proposal to colleagues in legislative language or prepared to ask for a formal vote on its ideas.

Asked if the group might do so and provide a meaty proposal that members could use to show their backing for the painful choices a big deal would require, Warner said the supercommittee must first reach its Thanksgiving eve deadline.

“We need to give the supercommittee time to finish their work,” he said.

And there were differences in opinion among the group’s members about whether they would be equally willing to back a small deal that merely hit the committee’s $1.2 trillion legal mandate.

Rep. Tom Rooney (R-Fla.), an organizer of the group in the House, said the group’s secondary message, besides that the deal should be broad, is that there is a group of rank-and-file members who want success.

“If it’s $1.2, it’s $1.2. That’s a hell of a lot better than sequestration, in my opinion,” he said.

But Rep. Heath Shuler (D-N.C.), another organizer, said it is too early to discuss whether the group would support a smaller proposal, on the order of $1.2 trillion to $1.5 trillion.

“We need to get to that $4 trillion mark now. If not, $1.5 trillion, I think hurts the markets, hurts the confidence of the American people,” Shuler said. “And if they don’t have confidence in what’s happening in Washington, they’re certainly not going to have confidence in investing in the future…We have to go big. It’s unacceptable to do anything but $4 trillion plus.”