WASHINGTON — With a handful of genuinely undecided voters holding sway in a tight race, Wednesday’s Denver debate will likely determine the next President. One way or another, debates are almost always decisive. Just ask Texas Gov. Rick (Oops) Perry — who couldn’t remember a cabinet agency he’d shut down in this year’s GOP primaries — or veterans of Gerald R. Ford’s 1976 campaign. At the second debate, in San Francisco, Ford made a lethal unforced error, declaring, “I don’t believe that the Poles consider themselves dominated by the Soviet Union.” The first question asked at a postdebate press conference...