Nothing has come easily for the 110th Congress, and Congressional Democrats and the White House struggled on Tuesday to hammer out the final details of a $15 billion bailout for General Motors and Chrysler that would allow lawmakers to wrap up the year.

With Senate Republicans calling for deeper concessions before spending taxpayer cash, the near-deal between the White House and Democratic leaders remained in doubt.

Barring a quick breakthrough, a GOP filibuster threatened to tie up the Senate into the weekend, with the potential for spoiling holiday plans and Congressional delegation trips and making for a grumpy Capitol.

At press time, Democrats and the White House were close to announcing an agreement on final language, but Senate Democrats were reluctant to make any declarations because they had yet to get any significant support from GOP Senators.

“Republicans are playing it cool,” said one senior Senate Democratic aide.

Indeed, Senate Republicans seesawed Tuesday between refusing to speculate on their support until they see a final draft to laying out vague benchmarks that would need to be met to garner their votes.

“I want to support a bill that revives this industry,” Minority Leader Mitch McConnell (R-Ky.) said on the Senate floor Tuesday. “But I will not support a bill that provides the patient with taxpayer dollars yet doesn’t [require] the commitment that the patient change its ways so that future help isn’t needed.”

Though Democrats said McConnell had declined invitations to join their discussions with the White House, McConnell panned a Democratic proposal floated on Monday as not going far enough to force automakers to restructure.

Asked about his refusal to engage in negotiations, McConnell deflected the question Tuesday afternoon, saying, “Well, we’ll see what the product looks like when we get one, if they announce they’ve got one.”

There were a few Republicans taking a firm stand, but it was against the measure. Sen. John Ensign (R-Nev.) became the first to formally threaten a filibuster.

“It only takes one of us, and as it currently stands I’m prepared to hold it. Some major changes need to happen to that bill before it can go through,” he said Tuesday afternoon.

Ensign wasn’t alone. Sen. Jim DeMint (R-S.C.) issued a statement of support, saying, “Ensign is exactly right. This bailout will hurt taxpayers, it won’t help the economy, and it will prevent these car companies from becoming competitive. The only way for the automakers to survive is a complete restructuring that allows them to break free from the stranglehold of union bosses. If Senator Ensign insists on debate on this legislation, I’ll fully support him.”

Sen. Bob Corker (R-Tenn.) also told CNN’s “The Situation Room” that the legislation did not impose concrete demands on the United Auto Workers union, which he said had made the industry uncompetitive, and for the company’s bondholders to write down the company’s debt before taxpayers’ dollars are committed.

“We are missing a tremendous opportunity,” Corker said. But Corker predicted the votes would be there in the end to pass the bailout package.

Facing a GOP filibuster threat, Majority Leader Harry Reid (D-Nev.) vowed to keep the Senate in session as long as necessary to complete the legislation.

“We’re going to have a vote on this sometime. We can either have it sooner or we can have it later, but everyone should understand there will be no stalling us from not doing this,” Reid said on the floor. “We are going to complete this legislation. … That may mean we have to work this weekend.”

Despite Reid’s weekend session threat, he may have trouble keeping his own Members in town.

Several Senators have travel plans over the next week and a half — with two Democrats scheduled to leave Tuesday evening for a climate conference in Poland.

Sens. John Kerry (Mass.) and Amy Klobuchar (Minn.) are scheduled to be out of town through Friday at the climate talks, and Kerry is expected to travel on to Georgia, India, Pakistan, Afghanistan and Kuwait. He is not expected to return until Dec. 19, his spokeswoman said.

Reid hinted that there may be more CODELs next week as well that could diminish his ranks.

However, Vice President-elect Joseph Biden has not formally resigned his Delaware Senate seat, and a Biden source said he was prepared to return for a vote if Reid asked him to do so.

House Democrats who had hoped to announce a deal Tuesday instead showed up late for an afternoon press conference only to say that negotiations were continuing and they still hoped to have a deal in the coming days.

Staffers ordered takeout and planned to work into the night — again — in hopes of finishing a bill so that it could be presented to Congressional caucuses today.

House Majority Leader Steny Hoyer (D-Md.) still hoped to get a deal done this week.

“I don’t want to anticipate next week, but we’re prepared to get this done,” Hoyer said.

House Financial Services Chairman Barney Frank (D-Mass.) added that few were opposing the package outright given that this is “the worst economy since the Great Depression. … For most of us, the question is how to do it, not whether.”