Update 12/11 - 3:59PM ET:
Democratic National Committee chair Howard Dean issued a statement calling for Blagojevich's resignation:
The arrest of and complaint against Gov. Blagojevich raises serious concerns about his ability to effectively represent the people of Illinois. The conduct alleged represents a disgraceful abuse of the public trust. In the interest of the people of Illinois and all Americans, he should resign immediately. If he does not, I hope the Illinois legislature will take action.
Update - 6:20PM ET: All fifty members of the Democratic Senate caucus have signed Majority Leader Harry Reid's letter calling on Gov. Rod Blagojevich to step down from his post and refrain from appointing anyone to the vacated Illinois Senate seat, a source confirms.
The development is noteworthy on several fronts. It signals that the Democratic Party, led by the Nevada Democrat, is organizing a united front against allegations of corruption - though, on this matter, it would be remarkable had any Senator refused to sign the petition. More importantly, it indicates that the Democratic senators are prepared to exercise their constitutional authority to undo any move that Blagojevich may make before he exits office.
Because he is still, officially, the governor, Blagojevich has the power to appoint Barack Obama's replacement. Illinois officials have tried to take away such authority by passing legislation that would allow the seat to be decided by a special election. But Blagojevich could make the appointment before the bill becomes law. That said, the United States Senate has the power to reject his appointment - something that Reid threatened in his letter. The fact that 49 other Democratic colleagues, including Vice President-elect Joseph Biden and Secretary of State nominee Hillary Clinton, have signed this letter suggest that they are serious about pushing back against any 11th-hour Blagojevich move.
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Senator Harry Reid is drawing a fairly bold line in the political sand in regard to the ethical missteps surrounding Rod Blagojevich.
On Wednesday, the Majority Leader and Sen. Dick Durbin drafted a letter -- which they subsequently urged their Democratic colleagues to sign -- that calls on the Illinois Governor to not just remove himself from office but to "under no circumstance" make a last-minute appointment to fill Barack Obama's vacant Senate seat.
Should Blagojevich disregard these warnings, Reid and Durbin write, the Senate would "be forced to exercise our Constitutional authority under Article I, Section 5, to determine whether such a person should be seated."
The letter, obtained by the Huffington Post, was sent around to Democratic offices this afternoon. And it leaves very little wiggle room for potential signatories -- you either think Blagojevich should be gone or you don't.
"We write to insist that you step down as Governor of Illinois and under no circumstance make an appointment to fill the vacant Illinois Senate seat," the letter reads. "In light of your arrest yesterday on alleged federal corruption charges related to that Senate seat, any appointment by you would raise serious questions."
It is also the first public indication that the Senate will take constitutional provisions to untangle any political appointment made by the embattled governor -- a legal maneuver that various scholars have said is well within the body's rights.
One additional point to make: Reid isn't simply willing for the Illinois legislature to remove Blagojevich's power to appoint an Obama replacement -- something that various Illinois politicians have called for. He is asking very specifically for the governor to step down, a move that Obama said he too favors.
Here is the complete letter.
Dear Governor Blagojevich:
We write to insist that you step down as Governor of Illinois and under no circumstance make an appointment to fill the vacant Illinois Senate seat. In light of your arrest yesterday on alleged federal corruption charges related to that Senate seat, any appointment by you would raise serious questions.
It is within the authority of the Illinois legislature to remove your power to make this appointment by providing for a special election. But a decision by you to resign or to step aside under Article V of the Illinois Constitution would be the most expeditious way for a new Senator to be chosen and seated in a manner that would earn the confidence of the people of Illinois and all Americans. We consider it imperative that a new senator be seated as soon as possible so that Illinois is fully represented in the Senate as the important work of the 111th Congress moves forward.
Please understand that should you decide to ignore the request of the Senate Democratic Caucus and make an appointment we would be forced to exercise our Constitutional authority under Article I, Section 5, to determine whether such a person should be seated.
We do not prejudge the outcome of the criminal charges against you or question your constitutional right to contest those charges. But for the good of the Senate and our nation, we implore you refrain from making an appointment to the Senate.