WASHINGTON – It was the biggest rout since Agincourt. If you insist, since the Carter-Reagan debate. With a remarkable display of confidence, knowledge and nerve, Mitt Romney won the first 2012 debate going away.

Romney didn’t just demonstrate authoritative command of a myriad of domestic issues. He was nervy about it, taking the president on frontally, not just relentlessly attacking, but answering every charge leveled against him – with a three-point rebuttal.

And he pulled off a tactical coup by coming right out of the box to undo millions of dollars’ worth of negative ads that painted him, personally, as Gordon Gekko – rapacious vulture capitalist who doesn’t just lay off steelworkers but kills their wives – and, politically, as intent on raising taxes on the middle class while lowering them for the rich.

The Romney campaign had let these ads go largely unanswered. But a “kill Romney” strategy can only work until people get to see Romney themselves. On Wednesday night, they did. Regarding the character assassination, all Romney really had to do was walk out with no horns on his head. Confident, smiling and nonthreatening, he didn’t look like a man who enjoys killing the wives of laid-off steelworkers.

Not a very high bar, I admit. But remember: It’s President Obama who set the bar. And succeeded. Romney suffers from unprecedentedly high negatives (50 percent), the highest unfavorability rating at this late date for any challenger in the last three decades.

As to the policy, Romney finally got to explain to the 60 million Americans watching that he intends to lower taxes across the board, particularly for the middle class. As for the rich, he got to explain the difference between lowering tax rates and reducing tax payments. He repeated at least twice that the rich would continue to pay the same percentage of the tax burden, while lower rates would spur economic growth.

His success in doing this against a flummoxed Obama does more than rally the conservative base. It may affect waverers – disappointed 2008 Obama supporters waiting for a reason to jump. They watch Romney in this debate and ask: Is this the clueless, selfish, out-of-touch guy we’ve been hearing about from the ads and from the mainstream media?

And then they see Obama – detached, meandering, unsure. Can this be the hip, cool, in-control guy his acolytes and the media have been telling us about?

Obama was undone on Wednesday in part by his dismissive arrogance. You could see him thinking annoyedly: “Why do I have to be onstage with this clod, when I’ve gone toe-to-toe with Putin?” (And lost every round, I’d say. But that’s not how Obama sees it.)

Obama never even pulled out his best weapon, the 47 percent. Not once. That’s called sitting on a lead, lazily and smugly. I wager he mentions it in the next debate, more than once – and likely in his kickoff.

On the other hand, Obama just isn’t that good. Not without a teleprompter. He’s not even that good at news conferences – a venue in which he’s still in charge, choosing among questioners and controlling the timing of his own answers.

By the end of the debate, Obama looked small, uncertain. It was Romney who had the presidential look.

Re-election campaigns after a failed presidential term – so failed that Obama barely even bothers to make the case, preferring to blame everything on his predecessor – hinge almost entirely on whether the challenger can meet the threshold of acceptability. Romney crossed the threshold Wednesday night.

Reagan won his election (Carter was actually ahead at the time) when he defused his caricature as some wild, extreme, warmongering cowboy. In his debate with Carter, he was affable, avuncular and reasonable. That’s why with a single aw-shucks line, “There you go again,” the election was over.

Romney had to show something a little different: That he is not the clumsy, out-of-touch plutocrat that the paid Obama ads and the unpaid media have portrayed him to be. He did, decisively.

That’s why MSNBC is on suicide watch. Why the polls show that, by a margin of at least two-to-one, voters overwhelmingly gave the debate to Romney.

And he won big in an unusual way. This could be the only presidential debate ever won so definitively in the absence of some obvious and ruinous gaffe, like Gerald Ford’s “there is no Soviet domination of Eastern Europe.”

Romney by two touchdowns.

© 2012, The Washington Post Writers Group