Why? First, to reward the Republicans for being obstinate. Obama has tried to work with the GOP, but has been repeatedly snubbed even by the moderate ones from Maine. If they want Obama to compromise, they need to as well. And that seems unlikely in the leadup to the mid-term elections, especially given what I said in my earlier post.
“No matter who he sends up,” Ms. Aron said, “I think Republicans are loaded for bear and will oppose.”Second, Obama has been frustrating the left for the entire year in office--reinforcing in Afghanistan, bailing out the banks, being slow on gays in the military, passing a health care bill that didn't have a public option, etc. This would be the one big win they could get, and they would care far more about the "correct" selection here than pretty much anyone else that might vote for Obama and the Democrats. Moderates are unlikely to vote on this issue in the fall, but turnout on the left will be deflated or energized based on this choice.
Third, the court is in the balance (as it always is). Replacing Stevens with a moderate would be bad for the long-run.
So, Mr. President, give your supporters when they want and teach your opponents that reciprocity works both ways.