The “Gang of Six” talks on deficit reduction broke down after Senators Dick Durbin and Tom Coburn got locked in a heated yelling match over Coburn’s demand for extremely deep cuts in Medicare that Durbin thought would “destroy” the popular program, a Senate aide familiar with the talks tells me.

The episode could prove at least somewhat reassuring to liberals who have worried that Durbin is open to a “grand bargain” that would include serious cuts in the popular program, which would undercut Dem efforts to draw a sharp contrast with Republicans on the issue. Durbin has insisted he’s at the “Gang of Six” table mainly to protect liberal priorities.

The episode also is a reminder of how much Republicans will insist on in Dem concessions as conditions for any deal.

According to the aide familiar with the talks, the senators got into a heated argument on Monday night, after Coburn demanded an additional $130 billion in Medicare cuts on top of the $400 billion in Medicare cuts recommended by President Obama’s fiscal commission, for a total of $530 billion in cuts for current recipients.

The Huffington Post reported yesterday that the additional amount sought by Coburn was $130 billion, and that the number represented a new demand. TPM’s Brian Beutler put the figure at $150 billion.

“Coburn came in on Monday and said, `I want $130 billion,’” the aide says. “The conservation was heated. There was yelling. Durbin said, `I am not doing this. That destroys Medicare. That goes even further than Paul Ryan. We’re not doing it.’”

The conversation went on for three hours or so, the aide says, but the senators could not break the impasse. “Because Coburn couldn’t get his way, he walked,” the aide says. Coburn called Durbin on Tuesday to tell him he was pulling out.

Coburn is thought to be one of the few GOPerswho can sell other Republicans on the need for revenue increases, or even tax increases, as part of a deal to close the deficit. But Coburn is under intense pressure from the right not to make any deal on revenues. The episode involving Coburn suggests there’s no way Republicans will go along with any revenue-enhancing deal without in­cred­ibly deep cuts to entitlements, particularly Medicare. And it illustrates that the only route to a deal may be if Dems make concessions that are truly enormous — ones it appears Durbin will not be willing to make if they fundamentally alter the program.

UPDATE: Coburn spokesman John Hart emails a response:

I’m not going to comment on his private conversations with his colleagues. Dr. Coburn had numerous concerns with the state of the Gang of Six proposal. As the Trustees recently concluded, Medicare is going bankrupt and will be destroyed if we do nothing. If the group wants to release their proposal to save Medicare and achieve long-term deficit reduction they are certainly welcome to do so.