Honestly and unfortunately, I think a little less of Tim Thomas for this. Whether you agree with the president or not, out of respect for the office of the Presidency I believe you should show up to something like this no matter what. It reminded me of a quote I heard from a soldier's mother who died in Afghanistan during the Bush presidency...."My son would not vote for President Bush, but he would take a bullet for him". (I know, that is an extreme example, but still, the principle).
He is asked to go shake hands with the President, not become best buddies with him. The 2nd American MVP in playoff history, and he protests by not showing up to the White House with every other teammate.
I'm sure there will be support on both sides, interesting to hear your opinions.