WHAT DO YOU want to achieve in a presidential debate? You want to hammer home your campaign themes. You want to put your opponent on the defensive. You want to sell yourself personally. And you want to avoid a gaffe or a damaging sound bite. Bush did all four in Wednesday night's third and final nationally televised debate with John Kerry. It was his best debate performance ever and that includes his three debates with Al Gore in 2000. As a result, it may have won Bush a second White House term.

Let's examine the four goals the president--or Kerry, for that matter--sought to realize in the debate. Themes? Bush's chief message was that Kerry is a liberal on the fringe of the political mainstream. He argued it with humor, saying Kerry is so liberal he makes Teddy Kennedy "the conservative senator from Massachusetts." And he did it by pointing to issues. He contrasted his tax cutting with Kerry's penchant for raising taxes. He insisted that Kerry's vote against the Gulf War in 1991 meant America could never pass the senator's "global test" for military intervention. In that war, the United States had the United Nations and most of the world were on its side, but not Kerry, Bush noted.

And for the first time, Bush made an effective case for a constitutional amendment protecting traditional marriage. Kerry claimed correctly that he and Bush agree marriage should only be between a man and a woman. But they don't agree on how to preserve

Defense? Kerry was forced to play defense last night as much as Bush was in the first debate two weeks ago. Kerry repeatedly said his health care plan was not a big government program. He all but admitted he has litmus test for prospective Supreme Court justices on abortion--that is, they must be pro-choice. Responding to Bush's charge he'd sponsored only a handful of bills during his 20 years in the Senate that actually began law, Kerry came up with an inaccurate claim to have "personally written" 56 bills.

Sell yourself? Bush looked comfortable during the debate's 90 minutes and acted as if he would happily have continued for another hour. Maybe this was because the debate didn't go beyond his normal bedtime (9:00 p.m. or so). Of course, his adjustment to Pacific time--the debate was in Arizona--would have had to be a quick one. Anyway, his answers on his Christian faith ("I pray a lot.") and what he's learned from the women in his life ("Listen to them.") were appealing. Also, again unlike in the first debate, his body language was positive.

Finally, there wasn't a gaffe or a major flub. A bad sound bite can be quite embarrassing when broadcast over and over on TV. Just ask Dan Quayle or Michael Dukakis. Bush didn't fall into that kind of trouble, nor did Kerry.