DES MOINES, Jan. 3 — Senator John Kerry reached into the past on Saturday with an endorsement — and a 10-minute song of tribute — from Peter Yarrow, a member of the folk group Peter, Paul and Mary. But the mini-celebrity moment took a turn when Mr. Yarrow, a peace activist since before the two men met protesting Vietnam, was asked if he was disturbed that Mr. Kerry voted in favor of war in Iraq. "Absolutely!" Mr. Yarrow shouted to a questioner, and he raised his hands to try to command the attention of reporters and Kerry supporters at the...