The circumstances and the issues may be different, but once again Congressional Democrats are poised to spend the days before Christmas locked in an intraparty squabble over a top domestic priority.

Last year’s health care reform marathon saw the public insurance option — a top liberal priority — whittled away. This year, the fight among Democrats is over the pieces of a $900 billion tax cut package brokered by President Barack Obama that includes controversial items such as estate tax relief and tax cuts for upper-income Americans. And none of liberals’ other wants — such as ending “don’t ask, don’t tell” or passing the DREAM Act for illegal immigrants — have been able to break through Republican opposition.

The Senate took its last vote on Christmas Eve last year, and at least one chamber could easily find itself in a similar position this year.

In many ways, the endgames of 2009 and 2010 are mirror images. While last year’s health care debate dragged on because of moderate unrest over Senate Majority Leader Harry Reid’s health care blueprint, this year’s final fight comes from the Democrats’ left flank, with liberals outraged over what they see as Obama’s tax cut giveaway.

The internecine rebellion boiled over last week in the House, where the Democratic Caucus resolved not to bring up a bill unless changes were made — and one frustrated Member even muttered “F— the president” during one of the party’s closed-door meetings.

And across the Dome, Sen. Bernie Sanders spent Friday mounting an hours-long crusade to build opposition to the package, including the payroll tax deduction that the president touted as good for the middle class. “Trust me, it is not to put more money in the pockets of working families; it’s the ultimate destruction of Social Security,” he charged.

Sanders was joined by several Democrats, including Sen. Sherrod Brown (Ohio) who, in an exchange with the Vermont Independent, argued, “Why would we continue an economic policy that clearly didn’t work for this country?” during the Bush administration.

Even moderate Sen. Mary Landrieu (D-La.) took a turn. During a Friday colloquy with Sanders, she argued that the agreement “borders on moral recklessness.”

But the deal appears to be gaining momentum anyway. Reid set up a procedural vote for today on a slightly tweaked version of the measure, which as of Sunday afternoon had secured the support of at least 18 Democratic Senators.

Reid was following Obama’s lead, even though he, too, had problems with the package and wasn’t directly involved in its crafting. Several Democratic aides said that while Reid knew Vice President Joseph Biden was negotiating with Minority Leader Mitch McConnell (R-Ky.), the Nevada Democrat had assumed the White House would deliver a compromise much friendlier to Democrats. Like many of his colleagues, Reid was surprised to learn that items like a generous estate tax provision were included.

Reid has said he will support the measure, and he’s joined by a diverse coalition from his Conference, including Sens. Bob Menendez (N.J.), John Kerry (Mass.), Jay Rockefeller (W.Va.), Daniel Akaka (Hawaii), Michael Bennet (Colo.), Blanche Lincoln (Ark.), Joe Manchin (W.Va.), Jim Webb (Va.), Max Baucus (Mont.), Joe Lieberman (Conn.), Kent Conrad (N.D.), Ben Nelson (Neb.), Evan Bayh (Ind.), Bill Nelson (Fla.), Tom Carper (Del.), Claire McCaskill (Mo.) and Bob Casey (Pa.).

All but two Republicans — Sens. Jim DeMint (S.C.) and George Voinovich (Ohio) — are expected to vote for the bill, and Reid is within three votes of being able to break Sanders’ filibuster, a hurdle most believe he will easily overcome.

The path forward in the House remains murky. Backers of the compromise such as Rep. Shelley Berkley (D-Nev.) predicted last week that the House will have to accept the Senate bill without amendments, and she expects Speaker Nancy Pelosi (D-Calif.) will ultimately bring the bill to the floor. Pelosi said last week she would respect the vote of her Caucus to keep the bill off the floor unless changes are made.

Opponents don’t appear to be satisfied yet.

“Dozens and dozens of House Democrats have real issues with something that will extend the Bush tax cuts,” one Democratic House aide said. “The question is can these folks feel as though they’ve made their voices heard so that there can be a vote in some way maybe to amend the bill.”

House Democrats could accept the Senate-passed bill, change it and force a conference committee or put it off to next year, an unsavory choice for many given the Bush-era tax cuts — particularly those for the middle class — expire on Jan. 1 and unemployment insurance benefits expired earlier this month. Some Democrats have suggested finding a separate measure to bring up alongside the tax package that would appease liberals.

“Right now there is not a lot of clarity on what the next step forward is on the legislative path except do what we can to strengthen and improve the bill the Senate would bring up,” the Democratic aide said.

But another senior Democratic leadership aide wasn’t optimistic about making significant changes to the final bill.

“I think what happens is if they make a couple of solid tweaks, we’ll swallow,” the aide said. “There is no doubt we’ll cave. We have nowhere else to go. It will be a question of how many votes we put up versus Republicans.”

While Democrats want to negotiate, they aren’t in a very good position, acknowledged the senior aide.

“In some ways House Democrats have put themselves on the sidelines,” this aide said. “We have one piece of leverage — the vote in caucus.”

And if House Democrats do get concessions, some House Republicans might walk away. Already some conservative groups were criticizing the final package as pork-laden and urging Republicans to hold out for a cleaner tax cut extension bill.

Anna Palmer contributed to this report.