Newt Gingrich makes much of the fact that he’s now 68 years old and a grandfather. The implication, I guess, is that he’s not going to be unfaithful to his current wife as he was with his previous two spouses. But it also defies common sense for us to conclude that at 68 years old a man can entirely remake his personality. Every day we see more evidence that he hasn’t changed a bit.

Rich Lowry writes: “The New Newt says he’s 68 years old and therefore has mellowed and matured. He was 65 years and a few months old when he opposed TARP and then supported it. He was still just 67 years old when he criticized President Obama for not instituting a no-fly zone over Libya and then criticized him for doing it. He was on the cusp of 68 when he denounced Paul Ryan’s Medicare reform as ‘right-wing social engineering,’ before contorting himself to explain it away.” The sense that he could, at any moment go wildly off the rails, is always lingering. “All that is predictable about Newt is that he is unpredictable, and, irresistibly, an election that should be about President Obama and his record will become about the heat and light generated by his electric performance. That’s the way it was as speaker, too. Eventually, he wore out his welcome in epic fashion.”

Part of why the “New Newt” myth is so transparently false is that he is incapable or unwilling to learn from his errors. At the onset of his campaign he brought down the wrath of the entire party by blasting Rep. Paul Ryan (R-Wis.) for allegedly engaging in “social engineering.” And wouldn’t you know it, that he did it again yesterday. Forbes reports that Gingrich rehashed his attack on Ryan in an online interview:

“I think you know that I like Paul Ryan, and you know that I’ve praised him a lot over the years. Callista has known him since he was an intern. And he and I talked after Meet the Press, which has been blown totally out of proportion. What I was saying was in answer to a very specific question, which was: if there’s a program which is very very unpopular, should Republicans impose it, and my answer was, no! When we passed welfare reform, 92% of the country favored it, including 88% on welfare. Reagan ran to be a popular president, not to maximize suicide. And I think conservatives have got to understand, you govern over the long run by having the American people think you’re doing a good job, and think you’re doing what they want. Now the question is, how do you have creative leadership that achieves the right values in a popular way?

Maximize suicide? Well, he doesn’t seem to be very remorseful for attacking a reform plan that every Republican House member voted for. Moreover, in his retelling, Gingrich entirely leaves out his “right-wing social engineering” comment, which was the flashpoint of the controversy. The report in full also details how poorly he understands Mitt Romney’s plan (which provide a Medicare option but within a defined contribution scheme). It’s the undisciplined, fact-challenged Gingrich that drove his party around the bend in the 1990s.

It is not surprising that Romney is drilling down on Gingrich’s inconsistency. The Post interviewed Romney, who seemed to echo Lowry and many of Gingrich’s harshest critics:

“He has been an extraordinarily unreliable leader in the conservative world—not 16 or 17 years ago but in the last two to three years,” Romney said. “And even during the campaign, the number of times he has moved from one spot to another has been remarkable. I think he’s shown a level of unreliability as a conservative leader today. . . .

“Let’s look at the record,” he said. “When Republicans were fighting for cap and trade and needed a leader to stand up against cap and trade, he did an ad with Nancy Pelosi about global warming,” he said. “When Republicans took one of the most courageous votes I’ve seen in at least a decade to call for the reform of Medicare under the Paul Ryan plan, he goes public and says this is a ‘right-wing social engineering’ plan. Even today he called it ‘suicide.’”

It is helpful to have an opponent who persistently illustrates your critiques.

Gingrich’s stubborn retention of a grab bag of unattractive personality traits also suggests that the Old Newt, hyper-partisan and passionate about many wacky things, won’t be trimming his sails in the general election. Already we see a mammoth gap in electability, reflecting the public’s conclusion that the Old Newt is the same as the New Newt.

The NBC/Wall Street Journal poll tells us:

Obama leads the former House speaker by 11 points among registered voters, 51 percent to 40 percent. But the president’s lead narrows to just two points against Romney, 47 percent to 45 percent.

Against a generic Republican, 43 percent say they will probably vote for Obama, while 45 percent say they will probably vote for the GOP candidate.

Why the difference between Gingrich and Romney? Look no further than their favorability ratings.

Gingrich enjoys strong numbers among Republicans (46 percent positive vs. 21 percent negative), conservatives (42 percent positive vs. 23 percent negative) and Tea Party supporters (54 percent positive vs. 16 percent negative). In fact, they are higher than Romney’s numbers among these same three key Republican groups.

But Gingrich struggles with other important voting blocs — like women (20 percent positive vs. 38 percent negative), independents (16 percent positive vs. 40 percent negative) and suburban residents (25 percent positive vs. 41 percent negative).

By comparison, Romney fares better among women (22 percent positive vs. 31 percent negative), independents (21 percent positive vs. 29 percent negative) and suburban dwellers (29 percent positive vs. 30 percent negative).

What’s more, 50 percent of registered voters say they would not vote for Gingrich in a general election — compared with 45 percent who said that about Obama and 44 percent who said that about Romney.

Likewise, a new Associated Press-GfK poll finds, “Among all people surveyed in the AP-GfK poll, including Democrats and independents, Romney fares better than Gingrich in head-to-head matchups with Obama. Obama and Romney are statistically even. But Obama leads Gingrich 51 percent to 42 percent.” In sum, Gingrich has a big electability problem.

You can’t teach an old dog new tricks, they say. And the general electorate thinks they’ve seen this dog before. Gingrich is his own worst enemy, and because he can’t change his essential nature or curb his worst instincts he is also a general-election disaster waiting to happen.