Complicating Democratic efforts to pass legislation like Don't Ask Don't Tell and the DREAM Act before the end of the current session, Sen. Ron Wyden, D-Ore., will undergo surgery for prostate cancer Monday, missing key Senate sessions next week and possibly over the coming weekend.

His absence could prove problematic for Democratic leaders in the Senate who can generally count on Wyden's vote in favor of most agenda items. With the $1.1 trillion omnibus spending bill now off the table and the Senate more likely to pass a continuing resolution to keep the federal government operating, Wyden's vote may not be as crucial to the Democrats as it could have been.

But with close votes on DADT and the DREAM Act looming before Christmas, the absence couldn't come at a worse time for the Democratic leadership. Sixty-one Senators have announced their support for a repeal of Don't Ask Don't Tell, and with Wyden's absence, the loss of a single Republican supporter would likely kill the measure.

Wyden says he was diagnosed with early stage prostate cancer in late November and decided to have the surgery done at Johns Hopkins Hospital on Monday. "I scheduled the surgery for the Monday before Christmas anticipating that the Senate would have recessed by that time and that there would be no disruption to my work in Oregon or Washington," Wyden said in a statement. "However, it now appears that I will be missing votes tomorrow and possibly next week while I prepare and undergo this procedure."

Even though the Oregon Senator says he expects a full recovery and to be back to work when the Senate reconvenes in January, some legislation Democrats are trying urgently to pass now may not stand a chance of getting through the Senate when new Republicans are sworn-in after the new year.