As senators attempt to wrestle this lame duck session to a close, with threats of extinguishing the Christmas holiday, priorities clashing with the dwindling calendar, and tempers flaring, one senior Senate Democratic leadership aide tells Fox all of this could lead to a government shutdown.

How could this happen?

The current stop-gap funding measure (called a Continuing Resolution - or CR, for short) that is keeping the government's doors open, employees paid, and the lights on expires on Saturday at midnight. The House passed a clean extension of the funding measure through fiscal 2011, but Senate Democrats, with the help of some of their Republican colleagues, have put together a $1.2 trillion omnibus spending measure that they want instead.

Many Republicans and a few Democrats have balked at the earmark-laden omnibus and have pledged to hold it up at all costs, though supporters have noted the pork accounts for less than 1% of the measure. Senate GOP Leader Mitch McConnell, R-Ky, who previously had earmarks inserted into the bill but now says he's opposed to the directed spending, said Wednesday that the chamber should, instead, pass a short-term CR to fund the government through February.

Senate Majority Leader Harry Reid, D-Nev, is expected to call up the omnibus sometime Thursday, and Republicans, including Sen. Jim DeMint, R-SC, are expected to pounce, demanding that the 1,924-page bill that was just introduced this week be read aloud by the clerks in the chamber, a move that is estimated to take about 35-40 hours.

That gets the Senate to sometime Saturday before Reid can even begin the procedural process to shut down the GOP filibuster. Once Reid files for cloture, a procedure that shuts down debate, technically there must be one intervening day before the cloture vote.

That would leave the government shut down on Sunday, as well as Monday, when the Senate would just be voting to end the blockade, a move that requires 60 votes. Final passage, technically-speaking, would then come after a 30-hour clock has run out, putting the Senate into late Monday or early Tuesday before final passage.

Then the measure must travel to the House, where House Republicans, staunchly against the earmarks in the omnibus bill, have vowed to work against the measure. More time must be expended to get to final passage there before the feds get their money.

If the government does shut down, this Democratic aide said, "It's not our fault," noting the GOP slowdown of the schedule.

One senior Senate GOP leadership aide took exception to that, telling Fox, "Talking about shutting down the government is not a win. We're two and a half weeks past the deadline for spending bills, and we're now on a treaty. We're not on a funding bill. And tomorrow morning, what will we be doing? A treaty. We didn't ask to go to the treaty."

All of that said, a number of aides on both sides of the aisle are expecting that cooler heads will eventually prevail, and the Senate will reach an agreement to wrap up the issue of funding the government by Saturday evening, in order to avert a government shutdown.

But -- this is the silly season...