The 2004 RNC Convention pretty much ended it for Kerry. Kerry's Convention gave him the smallest polling bump in history up until that point. Bush's Convention, especially Zell Miller's speech, was wildly successful.
Kerry choked like Hillary. He stood for nothing, ran for nothing, and his campaign was basically summed up with: Bush is a bad man. Never mind the fact, he voted for the Iraq War himself.
Kerry also never took off the gloves, he should of called Bush a liar on the Iraq War but just like with Hillary's inability to put away the phony email scandals...he played it safe and the right just tore him up for it.