In a 1969 case involving Adam Clayton Powell Jr., who was barred from the U.S. House of Representatives because of corruption allegations, the Supreme Court said that "in judging the qualifications of its members, Congress is limited to the standing qualifications prescribed in the Constitution" and that "since Adam Clayton Powell Jr. was duly elected by the voters of the 18th congressional district of New York and was not ineligible to serve under any provision of the Constitution, the House was without power to exclude him from its membership."
Nor does it matter that Powell was elected by his constituents and Burris was not. Its not Burris fault that there was no election. Like Powell, he secured his seat under the procedures set out by his state.
Its far more plausible to say that the Senate isnt obligated to accept Burris if his appointment involved illegality -- say, if he promised Blagojevich something tangible in exchange, as the governor allegedly sought from other prospects. But so far, no one has alleged, much less proven, anything of the kind. Its one thing for the Senate to conduct an investigation to remove all doubt. But it shouldnt use that pretext to endlessly delay what it cant legally prevent.
If the Senate thinks Blagojevichs presumption is intolerable, after all, it has another option, and one explicitly sanctioned by the Constitution: Seat Burris and then expel him.
The problem is that would require a two-thirds vote, and Republicans might not be willing to go along. For that matter, some Democrats might balk at inflicting such a harsh punishment on someone whose only sin is an excess of ambition and vanity -- which is not exactly rare in Washington.
When faced with a result that accords with the law, senators have a duty to accept it. In this instance, it wont be pleasant. But if the rule of law only told us to do what is pleasant, we wouldnt need it.