Senate Democrats have only one smart way to react Rod Blagojevich's impending appointment of Roland Burris to Obama's Senate seat: declare victory and go home.
Look at the plus side: by reacting strongly against Blagojevich's corrupt attempt to sell the seat, they stood up for political ethics, even against a member of their own party. The pressure on Blagojevich forced him to appoint an obvious place-holder who is qualified to hold the seat and who didn't buy it. (The $14,000 in contributions Burris made in 2002 can't in any way be seen as an attempt to bribe Blagojevich -- Burris would have to be Nostradamus on steroids to anticipate the series of events that led to the seat's becoming open.) So the right outcome happened in the end, or, at least, an outcome that wouldn't have raised a breath of opposition if all those juicy tapes hadn't been released in the interim.
Now think what would happen if the Democrats keep resisting. They can't block the appointment itself; the Supreme Court has ruled that the Senate (and House) can expel members, but they cannot prevent them from taking their seats in the first place. So the Senate would have to kick Burris out after he's already become a Senator, which feels quite different from stopping him from being seated.
Not only that, but say the Senate actually does expel Burris moments after he's sworn in. If Blagojevich is still in office, he could just reappoint Burris -- nothing would stop him from doing so. Then the Senate would be faced with the specter of kicking out Burris -- the only African-American Senator, mind you, after Obama's departure -- again and again. Or Blagojevich could find another Burris-like alternative who would try to take the seat, and the Democrats would have to kick them out too.
On the other hand, the Democrats could try to wait until Blagojevich is removed as governor, and then kick Burris out. But then Burris will have been a sitting senator for quite some time (anyone care to bet how long it will take until Blago actually leaves office?), and expelling him will still look bad.
Having gone through this thought exercise, the way forward is clear. The Democrats should hail Burris as a fine, upstanding man, worthy of holding the seat through his long years of public service, pat themselves on the back for pushing back against corruption, and call it a day. The only real question, now, is whether they have the insight and discipline to follow the script.