A lone senator could push the nation past the Oct. 17 debt-limit deadline even if a bipartisan deal is reached.
Senate leaders on Monday indicated they are inching towards a compromise deal to fund the government and raise the nation's $16.7 trillion borrowing cap before the nation is at risk of default.
Treasury Secretary Jack Lew has warned Congress the nation will be left with just $30 billion in cash by Oct. 17, and could be in danger of being unable to pay its bills beyond that point.
But if a senator or group of senators wanted to prolong the process as long as possible, experts warn, the Senate could blow right past that deadline even if there are enough votes to overcome a filibuster.
"People should recognize that it is going to be a major legislative effort to get any deal that's reached passed by the end of Thursday," warned Steve Bell, a longtime Republican Senate staffer who is now with the Bipartisan Policy Center.
"If [senators] want to really be as obstreperous as the rules of the Senate would allow them, I don't think you could pass a deal ... until the weekend," said Bell. "That's the worst case scenario."
Sen. Ted Cruz (R-Texas) did almost everything he could to delay work on a continuing resolution to fund the government, even holding a 21-hour speech on the Senate floor.
Cruz on Monday declined to say whether he could get behind a deal that didn't make significant changes to ObamaCare, and wouldn't give any indication as to whether he'd try to block it.
"We need to see what the details are first," Cruz said.
Sen. Joe Manchin (D-W.Va.), who has been involved in compromise talks with centrist members, said Monday the contours of a final deal could influence whether conservative senators like Cruz or Sen. Mike Lee (R-Utah) tried to slow it down.
Sen. Patrick Leahy (D-Vt.) acknowledged that passage of a deal could take a while due to procedural tactics.
"If we had grownups who care more about the country than their own political future and the kind of fundraising they can do from a small ideological group, then I'd be very confident," he said.
The Treasury has not said the government would default Friday without a debt-limit boost, but warned that it could no longer guarantee the government would be able to pay all its bills on any given day.
At best, many outside experts believe the government could pay all its bills until Nov. 1, when roughly $60 billion in payments on things like Social Security and Medicare come due.
— Erik Wasson and Bernie Becker contributed.