By Joe Warminsky, CQ Staff

The Senate Democratic Caucus sent a letter to Illinois Gov. Rod Blagojevich on Wednesday insisting that he step down and not appoint anyone to fill the Senate seat of President-elect Barack Obama .

The Democratic governor was arrested Tuesday on federal corruption charges for allegedly trying to trade Obama’s seat for favors. The 50 members of the Democratic Caucus said any appointment “would raise serious questions.”

“We do not prejudge the outcome of the criminal charges against you or question your constitutional right to contest those charges,” the senators wrote. “But for the good of the Senate and our nation, we implore you to refrain from making an appointment to the Senate.”

If Blagojevich were to make appointment, the senators said they would use their constitutional power “to determine whether such a person should be seated.”

State Democratic officials are scrambling to come up with a way to strip Blagojevich of his right to name Obama’s successor if he does not voluntarily resign or temporarily step aside.

A committee of the Illinois state House is scheduled to meet Dec. 15 to take up legislation establishing a process for a special election to fill the seat. It is also possible that Blagojevich will face impeachment proceedings.

The Democratic Caucus includes Vice President-elect Joseph R. Biden Jr. , D-Del., who has not yet resigned his seat, as well as two independents who side with Democrats in forming the Senate majority.

Obama also has called on Blagojevich to resign.