When Obama clearly states his intentions as follows, I have doubts about his ability to pick the Justices.
"Obama has an entirely different perspective. His spokesman, Tommy Vietor, stated that Obama "has always believed that our courts should stand up for social and economic justice." Indeed, Obama has said he wants justices who have "the empathy to recognize what it's like to be a young teenage mom," or to be gay, poor or black. Many liberal legal scholars agree, although they use other labels as synonyms for empathy and social consciousness.""
What does that have to do with interpreting the Constitution?
It has nothing to do with interpreting the Constitution. So, since Obama's surrogates claim that he was a "Constitutional law professor", we have to assume that he does know something about the Constitution, and we also have to assume that the Constitution won't factor into his SCOTUS picks should he have that opportunity.
At the Saddleback interview, he said he wouldn't have nominated Roberts, Scalia, Thomas, or Alito. That means we can expect a lot more judges like Stevens, Ginsberg, and Breyer, none of which have any reluctance to legislate from the bench. With a whole court of that kind of justices, the Constitution will have no defenders or protection at all.