The Senate voted largely along party lines on Sunday afternoon to block legislation crafted by Senate Majority Leader Harry Reid (D-Nev.) that would raise the debt limit by $2.4 trillion.
Reid and other Democratic leaders worked intently to persuade centrist Republicans to support the plan but fell short.
Sen. Joe Manchin (D-W.Va.), Sen. Ben Nelson (D-Neb.) and Sen. Bernie Sanders (I-Vt.) voted against Reid's plan, as did Reid himself in a procedural move that allows him to bring it back to the floor.
Sen. Jim Inhofe (R-Okla.) was the only senator to miss the vote.
Lawmakers say they have been told the president and GOP leaders are closing in on a deal and expect one as soon as Sunday.
Reid had told colleagues shortly after noon that he was cautiously optimistic about the negotiations.
"We are close to an agreement with Republican leaders," he said. “[A]fter speaking to Republican leader Mitch McConnell (R-Ky.) this morning, we are cautiously optimists.”
Senators will wait for a bipartisan deal to be finalized and then will begin work on advancing it to the House.
Reid signaled to colleagues that they could begin moving it as soon as Sunday.
“I would not suggest [going to] a ball game,” said Reid from the floor to some laughter. “Maybe closer than that.”
“But we'll give everyone adequate notice,” the majority leader assured members.
Democratic senators joined Reid Sunday afternoon for a special caucus
meeting to hear about the status of negotiations with GOP leaders on
the latest compromise attempt.
Senate leadership emerged from the meeting shortly after 4:35 p.m. The senators did not comment on their discussions.
When asked if a vote was possible on Sunday evening, Reid said "I hope so."
If any senator decides to object and drag out proceedings, Congress will not make the Aug. 2 deadline set by Treasury Secretary Timothy Geithner.
A Democratic aide said that if conservatives filibuster the deal, the soonest it could pass the Senate would be Wednesday.
Senate conservatives however say they don't have plans to delay consideration of a possible bipartisan debt-ceiling agreement.
Sen. Mike Lee (R-Utah), a member of the Senate Tea Party Caucus, said he would insist that any compromise receive at least 60 votes on the Senate floor but not drag out the process to delay an agreement beyond Tuesday.
Reid is expected to use a message from the House as the legislative vehicle to pass a deal through the upper chamber.
But doing so would still require the Senate to spend Monday, Tuesday and part of Wednesday processing it unless every senator agrees to truncate the timeline.
A stopgap measure may be necessary to allow the government to pay its bills after Aug. 2. But such a Band-Aid would need to receive unanimous consent to pass by Tuesday.
This story was posted at 1:38 p.m. and has been updated.