Updated: Feb. 25, 10:46 p.m.

Retiring Sen. Jim Bunning (R-Ky.) late Thursday launched a one-man crusade to block an extension of unemployment and COBRA insurance benefits, vowing to allow the benefit programs to expire Sunday unless Democrats agreed to pay for them with unused stimulus funds.

Bunning’s quixotic pursuit of deficit offsets at the potential expense of payments to unemployed or uninsured citizens enraged Majority Whip Dick Durbin (D-Ill.) and other Democrats, who vowed to keep the chamber in session until Bunning relents or collapses.

A senior Democratic leadership aide said Durbin would ask for unanimous consent to pass the extensions without Bunning’s payment scheme every half hour for the foreseeable future. “We’re going to keep doing it until we break him,” the aide said.

Democratic and Republican aides agreed that Bunning’s decision was made unilaterally, noting that Bunning and Minority Leader Mitch McConnell (R-Ky.) have essentially not been on speaking terms for more than a year.

“McConnell doesn’t have any sway over him,” a senior Democratic aide said, and GOP aides stressed Bunning’s opposition is not a coordinated GOP position.

Indeed, Republican and Democratic aides said McConnell and Majority Leader Harry Reid (D-Nev.) worked out a deal Wednesday under which Reid would allow Bunning to offer an amendment requiring the extensions be paid for prior to approving them.

But Bunning rejected that deal because it was all but certain that a majority of the Senate would handily defeat the amendment.

“Of course, we can have a vote on it, and, of course, it can be defeated, and then, of course, we can pass the bill without the money. I am not willing to risk that $10 billion being added to the deficit. I was not ready to risk voting on a bill I knew would not get the amount of votes necessary to pay for it. If the Majority Leader would have included it in his UC, I would have had no problems. But he did not include it in his UC. So that was the reason I asked to pay for it,” Bunning said on the Senate floor Wednesday.

If Bunning is successful, it could prove to be a significant blow to the GOP. Unemployment and COBRA health insurance benefits are popular, and with the unemployment rate soaring, lawmakers have been keen to ensure there are no interruptions in payments.

Should the programs lapse, Democrats could use the episode to tar Republicans as unconcerned with the poor.