Why Would 19 GOP Senators Oppose This?

Yesterday we learned that two of our soldiers in Iraq were killed and likely tortured beyond recognition. In the raw emotion of these events, the U.S. Senate acted in a rarely bipartisan fashion. They passed an Amendment that said the following:

"To express the sense of Congress that the Government of Iraq should not grant amnesty to persons known to have attacked, killed, or wounded members of the Armed Forces of the United States."

Seems reasonable enough to me. The inexplicable point is that what should be a slam dunk amendment was opposed by 19 U.S. Senators. All of them Republicans, to include likely 2008 Presidential candidate John McCain of Arizona.

Now I did not hear debate on the issue (if there even was debate). But I am at a loss to explain their reasoning in voting against this amendment. Any ideas?