Six weeks ago, I wrote that in the GOP race for the presidential nomination, Mitt Romney's the one — mostly because the other candidates have proved to be implausible or utterly inconceivable. And after Wednesday's Michigan debate, we now know with even more certainty who the Republican nominee will be. His name is not Rick Perry, whose potential comeback imploded in an excruciating, alternately comical and pathetic 50 seconds that left an indelible impression of someone out of his depth — and all but out of the race.

A few million people watched the debate; perhaps 50 million had seen the excruciating 50 seconds by the next day. Perry, who initially led the race when he entered as the true conservative alternative to Romney, has biffed, farbled, and gaffed his way into the now inescapable status of an also-ran. It's over. When Perry was on that stage in Michigan, I was in a room with top Republican pros. One of them read a tweet out loud: "Campaign office furniture in Austin, Texas, now available on Craigslist."

Debates matter; they are often decisive, a truth Perry ignored as he decided to announce, but didn't prepare himself to run — and a truth Romney learned the hard way in his losing 1994 Senate campaign against Ted Kennedy. Perry's decline and fall has been so startling — and Tim Pawlenty's so swift when he refused in a New Hampshire forum to repeat to Romney's face a criticism he'd peddled on television just the day before — that there's a gathering consensus that debates are more critical this year than ever before.

Romney looks like a president. He more than anyone else commands the stage; in this field, he looks like the one who could go up against Obama.

At best, that's half right. The instant analysis of the mainstream media, with a few exceptions, used to be metronomically balanced; the voters made a judgment, but the press was reluctant to rush to judgment, preferring to wait for the next set of polls, or hedging any verdict with ritualistic qualifiers. What's different this year is social media, which does not wait and which has pushed tradition outlets to keep pace. But the reality of debates as game changers is as old as the 1960 clash between John F. Kennedy and Richard Nixon.

In Chris Matthews' lyrical new book Jack Kennedy: Elusive Hero — which draws you into the character of that extraordinary man and time so you almost feel you are there — there is a riveting account of the first televised presidential debate in American history. Kennedy drilled, lying on a "bed in his hotel room, clutching a fistful of cards in his hand… After each card has been dealt with, Kennedy would throw it on the floor." He met Dan Hewitt, the CBS producer who would later create 60 Minutes, a week before the debate in "a hanger at Chicago's Midway Airport" to learn about the staging and stagecraft of the encounter. "Kennedy took the thing much more seriously than Nixon," Hewitt said. Kennedy prepared; Nixon showed up. And that was the making of the president in 1960.

Ever since, debates have turned tides — in general elections and primaries alike. Thus in 1976, Gerald Ford rhetorically freed Poland from Communist domination — and lost the White House. Four years later, after strategically using his debate with Jimmy Carter to reassure Americans of his commitment to nuclear arms control, Ronald Reagan closed the deal as he rebuked Carter: "There you go again."

In 1992, the first George Bush blew his diminishing prospects for re-election when he impatiently glanced at his watch; in 2000, Al Gore was branded a loser for sighing during his confrontation with the second Bush — which Gore otherwise clearly won. And in 2004, John Kerry asked a devastating question in an Iowa debate: "Governor Dean, you recently said that you wouldn't presume that Osama Bin Laden was guilty for 9/11. What in the world were you thinking?" There was no good answer. The press barely noticed the exchange; but for Iowa Democrats, it crystallized the race. They wanted someone who had a real chance to beat Bush — and it wasn't a candidate who'd said something like that.

I doubt Perry knows that history, and it's probably too late for him to read Matthews' book. He's either treated the debates as a drop-by or he's incapable of getting ready — which means he's not ready to take on Barack Obama or to grapple with the demanding decision-making of the presidency.

Romney is a different case. He doesn't have to read about debates. In that 1994 race with Ted Kennedy, Romney kept demanding one; unfortunately for him, he got what he wished for.

Romney had been accusing the Kennedy family of a sweetheart land deal to locate a mega furniture mart in Washington, D.C. It was negative research gone awry: The parcel was in a depressed area and the project would become a centerpiece for redevelopment. It had been purchased by a blind trust; Kennedy didn't even know about it. But that wasn't the point he chose to make. Voters simply didn't credit the notion that he was in politics to feather his own nest. So when Romney complained about Kennedy's criticisms of his business record, Kennedy cited the Romney ad about the sweetheart deal and said directly to him: "Mr. Romney, the Kennedys are not in public service to make money. We have paid too high a price." The applause rocked the debate audience at Faneuil Hall.

Almost three million people in Massachusetts were watching as a flustered Romney later tried to insist, almost plaintively, that he did too favor a woman's right to choose. Kennedy shot back: "You're not pro-choice, but multiple choice."

Romney had led at the end of September; his debate performance, combined with ads that featured workers who had lost their jobs or seen their wages and benefits cut in his corporate takeovers, brought him to an 18-point defeat.

By the 2008 presidential race, Romney was better. He did slip up in one debate, when he proclaimed that he was the real candidate of change. John McCain responded that he sure was — he changed all the time.

So the Romney of this year benefits from a long learning curve. On stage with his opponents, he never leads with this chin. His missteps are minor: He told a lawn service he couldn't hire illegal immigrants because "for Pete's sake, I'm running for office." But he doesn't lead the dialogue; he lays back. And he fights back, for the most part confidently, when he's attacked. With his labored distinctions between ObamaCare and RomneyCare, he's skating on thin ice; but so far he's skated successfully.

He's stuck with his flip-flops; but in Michigan, he brushed them aside with a sermonette about his constancy to his family and faith. He wins the debates by not losing. He's occasionally brittle and sometimes his body language is awkward. But Romney looks like a president. He more than anyone else commands the stage; in this field, he looks like the one who could go up against Obama.

It's a fallow field. Think of the contrast with the GOP choices in 2000. Instead of a pre-certified Bush, there's a self-destructing Perry. Instead of a heavyweight flat-taxer like Steve Forbes, there's Herman Cain — who, whatever his apologists say, is fumbling and (apparently) lying his way toward a well-deserved defeat for a clearly unqualified candidate. Instead of a genuine maverick like John McCain — and he was one in 2000 — there's the re-tooled revisionism of Mitt Romney.

The Right is suspicious of that, and the search for the un-Romney will continue for awhile. Newt Gingrich may have his nano-second in the spotlight; he's about all that's left unless Jon Huntsman, the Obama-tainted former ambassador to China, can pull a nearly incredible upset in New Hampshire. But Gingrich is as unthinkable as those who have gone before — say, Michele Bachmann — and those who are never going anywhere — like Rick Santorum and Ron Paul, who's confined to a cranky libertarian cul de sac.

The field's weakness is Romney's strength. He can and ultimately will get past right-wing resistance by saying whatever he has to. In this last debate, when asked about the Eurozone crisis, he joined in a chorus of economic isolationism reminiscent of the Republican isolationism before World War II: What happens in Europe doesn't matter to us. As CNBC's Jim Cramer observed, collapse there could be catastrophic for our economy and our banks. The debate was a parade of conservative bromides, not a serious discussion of serious issues. 

Finally, there are signs that while what Huntsman accurately called "pandering" is working for Romney with reluctant Republicans, its toxic side effects are seeping through to the general electorate. Not only does Obama lead Romney nationally by 6 percent in the latest NBC/Wall Street Journal poll; according to a PPP survey in Ohio, the state that historically winning Republicans need to carry, Obama's lead is 9 percent. How do you explain this when voters feel the country is so far off on the wrong track? Well, in Ohio, Romney's favorability rating is 28 percent, and his unfavorable mark is 48. He increasingly morphed into a product re-engineered to fit the shifting marketplace of his long-time business plan to takeover the presidency.

What a contrast with Matthews' description of Kennedy — "an inner-directed self-creation… a serious man who was teaching himself the hard discipline of politics until the last minute of his life."

Mitt Romney has learned enough of that discipline to win the debates — and the nomination. But he feels and sounds like a construct. Will he ever convincingly come across as serious about anything but himself?