He ignored the issue all together.
I'm watching Letterman last night, very briefly, and I see Dave ask one of his softball questions, "If you were elected president in 2000, would you have gone to war in Iraq?" Then he proceeded to clarify, if Kerry had had the information Bush did at the time, would Kerry have gone to war.
Kerry took the next two minutes explaining to America how voting to authorize the president to go to war doesn't mean he wanted to go to war. Then he explained what he would do in Iraq if elected this time. Then he explained why he didn't vote for the money to support the troops. Then he explained again what he would do if elected, again.
Never did he answer the question, or come remotely close to it.
Nice work, senator.