This report is spinning this as a test of to see where the Republicans stand. They better stand with the troops or face being in the minority for years to come:

Bruised by the elections and divided on the Iraq war, Republicans will find themselves in a tough spot when Democrats force them to go on record for or against President Bush’s troop strategy.
Democratic House and Senate leaders intend to hold votes to gauge GOP opposition to Bush’s decision to send 21,500 more troops to Iraq. Senate leadership is expected by Thursday to propose a resolution denouncing the plan, with debate planned around the same time Bush delivers his State of the Union speech next Tuesday.
Majority Leader Steny Hoyer said the House will follow suit with its own resolution.
The resolutions would likely be a symbolic expression of Congress but would not affect the Pentagon’s war budget or challenge the president’s authority over U.S. forces. Such votes could be a shot across the bow to Bush, who said Jan. 10 that the extra troops are needed to protect U.S. interests in Iraq.
The resolutions also would help Democrats measure GOP support for more aggressive legislative tactics, such as cutting off funds for the war.
Such a vote puts many Republicans in an uncomfortable position. They will have to decide whether to stay loyal to an unpopular GOP president and risk angering voters disillusioned by the war or buck the party line.

There is another option here: angering the base by voting with the Democrats. Here are their choices, you support the president’s plan and show the enemy that you are behind him in a time of war or you vote with the Democrats and undermine his policy. Voting with the Democrats is a sign that they want to cut and run and leave Iraq to civil war and Iran and Syria and giving control of the oil fields to our enemies. That’s what they are voting on.
BTW, it is a political ploy to embarrass the president:

Acknowledging their party is divided on Iraq, Republican leaders are trying to stave off a showdown in Congress by casting Democratic efforts as a political ploy to embarrass the president. On Tuesday, House leaders offered GOP members a second day to air their concerns about Bush’s plan behind closed doors.

If this were Clinton proposing more troops, Congress would be following all over themselves providing support.
And will this be enough to appease their base?

House Democratic leaders say their approach will be simple: put Bush’s plan in a nonbinding resolution and subject it to a vote. If it fails, the House will be on record as rejecting the additional troops.

I don’t think so.