I thought Kerry voted in favor of the war.
You are correct, 'dat. He did.
But remember WHEN he did, even more important than THAT he did. (and the others, for that matter). Right before the 2002 "midterm" elections. Well, they are only "midterm" for the President. For the House of Representatives, every two years, they run for office, as does a third of the Senate...including Mr. French Toast.
They thought it would get them the House back, and keep their razor slim majority in the Senate. When neither one worked, it was carte blanche to fire away, figuring that the mainstream media would either cover up their previous vote/support for the war, or would amplify their current disdain for the war, and their political opponent who was/is the Commander in Chief of it. Both have proven true.