If he nominated Colin Powell, he would get confirmed and would get a solid liberal on the Court. Orrin Hatch, John Huntsman, John Kasich, Lamar Alexander . . . . All of them would be pretty easy confirmations and would give Obama 80% of what the hardest leftist judge would give him.
He isn’t going to nominate any of those people.
I'm pretty sure Powell doesn't have a legal background, nor even a law degree. No serious person could ever nominate, much less confirm someone like him as a Justice.