The GOP officially launches its last stand against health care reform today, when a united Republican Conference takes to the Senate floor in an effort to dismantle portions of the legislation with a variety of tactics.

Republicans are “virtually certain” there are flaws in the Democrats’ strategy that can be exploited to thwart the majority party’s plan for wrapping up health care legislation within the next few days, a senior Republican Senate aide said.

Meanwhile, President Barack Obama will be taking a victory lap — albeit a subdued one at least for now — today when he signs the core of the legislation cleared by the House late Sunday night.

After Obama signs that legislation into law, Senate Majority Leader Harry Reid (D-Nev.) will officially call up the health care reconciliation package, also passed by the House on Sunday night. The package is potentially vulnerable to a variety of procedural challenges — not to mention GOP amendments that some Democrats would find hard to resist.

The reconciliation package includes crucial changes to the health care legislation demanded by House Democrats.

The Senate Republicans’ maneuvering has been happening off the floor for days. Senate Republicans on Monday moved to topple the reconciliation package entirely, arguing to chamber Parliamentarian Alan Frumin that it violates the narrow rules governing such bills and should be subject to a filibuster.

The GOP hopes, at a minimum, to force the House to vote again on the measure.

Democrats, meanwhile, hope to clear the reconciliation package no later than Sunday, and leadership continues to push for party unity during the amendment process. The majority will attempt to put the Republicans on the defensive politically and make the case for the policy benefits in the legislation while defending the bill against GOP procedural attacks.

“At some point it’s out of our hands,” said Jim Manley, a top spokesman for Reid. “We will continue to make the best case we can, all the while trying to defeat any amendments or points of order.”

The reconciliation package is expected to drop on the Senate floor this afternoon. Senate Democrats expect the legislation’s allowable debate time of 20 hours to expire on Thursday, after which the Republicans are likely to unleash a flood of amendments in a “vote-a-rama” session. Under reconciliation rules, there is no cap on amendments, but with no debate time permitted on those amendments, Senators are likely to engage in one roll-call vote after another.

Reid has committed to the White House and House Democrats that at least 51 Democrats will support the legislation and send it to the president’s desk. But his toughest task might be holding his caucus together to vote against GOP amendments designed to be attractive to moderate Democrats.

Procedural War

Reconciliation rules, which allow for a bill to pass the Senate with a simple majority as opposed to the customary 60 votes, are governed by narrow guidelines that demand all provisions have direct deficit implications while inhibiting expansive policy changes.

Accordingly, Republicans plan to raise several points of order, and if Frumin sides with the GOP on any such efforts, Democrats lack the 60 votes required to overcome points of order. Even the smallest change to a reconciliation package requires that it be sent back to the House.

In particular, Republicans on Monday argued the legislation’s “Cadillac” tax on expensive health insurance plans affects Social Security and in doing so violates the Budget Act. Democratic and Republican staff made their arguments during a closed-door noontime hearing.

Meanwhile, Republicans also intend to propose dozens and possibly hundreds of amendments to the reconciliation bill — another part of their strategy to force the House to revote.

“I generally don’t predict the outcome of votes before we have them. There are going to be plenty of them, and we’re going to give it our best shot,” Senate Minority Leader Mitch McConnell (R-Ky.) said when asked how confident he was that Republicans could block reconciliation. “The American people are counting on us to stop this awful bill, and this is, sort of, even worse than the first bill.”

Democratic and Republican Senate staff are scheduled to meet with Frumin again as early as today, at which time the GOP is expected to argue for several budget points of order against provisions of the reconciliation package and ask for a ruling. The senior Republican Senate aide described the meeting as a “Byrd bath” because most of the points of order raised by the GOP will charge that the reconciliation violates the Byrd rule requiring that each provision of such legislation has direct deficit implications.

“We are virtually certain that there will be a handful of provisions that don’t clear that hurdle,” the aide said.

For Democrats, the challenges are twofold: enforce party unity and seize control of the political narrative.

The Senate Democratic leadership has been successful in obtaining commitments from their rank-and-file Members to vote down all Republican amendments, even those that might be politically problematic come November. However, one Democratic source said the leadership is still working to ensure that no Democrats propose amendments of their own.

Sen. Michael Bennet (D-Colo.), for instance, said last week that he was still considering whether to propose an amendment to add a public insurance option. The Democratic source predicted that party leaders might not achieve unity on this front but would be able to muster the votes needed to defeat any amendment proposed by one of their own Members.

Manley said the Democrats plan to focus public attention on the policy benefits in the reconciliation package and how it strengthens the underlying Senate bill. The majority also intends to highlight those reconciliation measures that it says have roots in proposals previously offered by the GOP.

“Our goal includes making the debate about people, not procedure,” Manley said. “And to ridicule the idea that the GOP would oppose a bill making fixes that they should support.”