If I had it, I’d bet a lot of money that Mitt Romney will be the 2012 GOP presidential nominee.

For reasons I’ll get to, I’d have said that even before last week’s debate at Dartmouth College, which I attended. But now I’m even more convinced.

Romney was cool. He was confident. He let no one slam him. He seemed knowledgeable and experienced. And he even showed some heart, which he hadn’t much up to now.

Most revealing were his answers when questioned by rivals Herman Cain and Newt Gingrich.

Cain wanted to know whether Romney could recite all 59 points in his economic plan, comparing it with the simplicity of Cain’s own 9-9-9 tax plan.

Romney: “Herman, I have had the experience in my life of taking on some tough problems. And I must admit that simple answers are always very helpful but oftentimes inadequate.”

Then he went on to tick off the standard GOP litany — low taxes, deregulation, trade, etc. — but added that “we also have to have institutions that create human capital. We’re a capitalist system. But we don’t just believe in physical capital or financial capital, but also human capital. We need great schools, great institutions.”

It was the only time any of the candidates even hinted that, besides slashing budgets, America might be in need of some investment.

Then Gingrich, implying that Romney was engaging in Obama-style “class warfare,” wanted to know why his plan would cut capital gains taxes especially low for people making less than $200,000 a year.

Romney: “Well, the reason … is that middle-income Americans have been the people who have been most hurt by the Obama economy. …

“Not only do we have 25 million people out of work or stopped looking for work … we just saw this week that median income in America has declined by 10 percent during the Obama years …

“And so, if I’m going to use precious dollars to reduce taxes, I want to focus on where people are hurting the most, and that’s the middle class.

“I’m not worried about rich people. They’re doing just fine. The very poor have a safety net. But people in the middle, the hardworking Americans, are the people who need a break, and that’s why I focused my tax cut right there.”

That sounds like a candidate who is not just interested in winning Republican primaries but a general election.

Again, when Texas Gov. Rick Perry raised the charge that Romney’s Massachusetts health care plan — “Romneycare” — was “Obamacare,” Romney didn’t flinch.

“I’m proud of the fact that we took on a major problem in my state,” he said. “The problem was that we had a lot of kids without insurance, a lot of adults without insurance. It added up to 8 percent of the population. We said, ‘We want to get those folks insured.’”

He said that wasn’t Obamacare because the president’s plan affects all Americans. “We have the lowest number of kids as a percentage uninsured of any state in America,” he told Perry. “You have the highest.” Perry was silenced.

When Perry tried to interrupt, Romney shot: “I’m still speaking. … We have less than 1 percent of our kids uninsured. You have a million kids in Texas uninsured.”

An NBC-Wall Street Journal poll taken just before the debate and a Rasmussen poll taken just after showed Romney tied with Cain, the former Godfather’s Pizza CEO. But Cain is not going to be the GOP nominee.

Why? Because the Republican Party always picks its presidential candidates by the rule of primogeniture — the next guy in line gets to be the king.

So, in 1960, Vice President Richard Nixon got nominated. In 1964, arguably the party abandoned the rule by nominating Barry Goldwater, but after he was wiped out, it went back to Nixon in 1968.

When Nixon resigned, he was succeeded by Gerald Ford despite a challenge from Ronald Reagan. After Ford lost, Reagan got nominated, and after his eight years, it was his vice president, George H.W. Bush.

And after Bush lost in 1992, the next guy in line was his 1988 challenger, Sen. Bob Dole (Kan.).

Maybe George W. Bush wasn’t next in line, but his name was Bush and he beat Sen. John McCain (Ariz). And when 2008 rolled around, the party ended up with McCain as the nominee, with Romney as the runner-up.

So I think it’s historically next to inevitable that Romney will be nominated.

And as to betting, Romney is who the oddsmakers favor, too. Ladbrokes in London has him at 8-to-13, Perry at 3-to-1, Cain at 8-to-1.

Intrade, the U.S. betting site, put Romney at 63.9 percent before the debate, 66.6 percent right after and 67 percent two days later. By the end of the week he stood at 66.9 percent. Perry fell from 13.9 percent to 9.6 percent. And Cain fell from 10 percent to 9.1 percent.

Bad reviews of 9-9-9 — it’s regressive, won’t raise enough revenue and creates a national sales tax — will finish off Cain, as will his endorsement of Alan Greenspan, father of the 2008 crash, as the best Federal Reserve chairman ever. Perry is monied but cratering.

And Romney is favored not only by the GOP “establishment,” but by New Jersey Gov. Chris Christie, who’s beloved by the tea party. And even Rush Limbaugh, while declaring Romney “no conservative,” says “I like him very much.”

So, I’d bet on Romney. But the odds are such that I wouldn’t win much money.