Mr. Blagojevich has a disability

If the Governor is unable to serve because of death, conviction on impeachment, failure to qualify, resignation or other disability, the office of Governor shall be filled by the officer next in line of succession for the remainder of the term or until the disability is removed.

Ill. Const. art. V, § 6(b) (emphasis added).

Argues Illinois Attorney General Lisa Madigan:

Just as impeachment or resignation constitutes a disability that renders an individual unable to serve as Governor, pending federal criminal charges of this nature and severity are a disability that has rendered Mr. Blagojevich unable to serve. As a result of the federal complaint relating to his official acts, Mr. Blagojevich's future official acts — many of which are the subject of the federal complaint — will be subject to challenge as illegal or improperly motivated. Because the integrity of Mr. Blagojevich's future official acts will be in question, his ability to provide effective leadership is eliminated.

There's a bit of speculation creeping into the logic there, what with the predictive aspects relating to Blagojevich's future acts, which the governor is seeking to head off at the pass through numerous appeals to a higher authority than the Illinois Supreme Court:

Shortly after [another three Baptist preachers had prayed and] left, a fourth minister, the Rev. Leonard Barr of Fellowship Missionary Baptist Church, arrived at the governor's house with his wife, Rita.

He said they were invited by the governor and that the two "prayed that he would continue to be a great governor for the state of Illinois."

Perhaps the latter, however, is an even larger presumption (or else a whole series of them). Still, you can't say that Rod R. Blagojevich doesn't have a prayer or three.

The legal attack to oust Blagojevich — Chicago Sun-Times