By Paul Krugman – The New York Times.

All the experts tell us not to pay too much attention to polls for another week or two. Still, it does look as if Hillary Clinton got a big bounce from her convention, swamping her opponent’s bounce a week earlier. Better still, from the Democrats’ point of view, the swing in the polls appears to be doing what some of us thought it might: sending Donald Trump into a derp spiral, in which his ugly nonsense gets even uglier and more nonsensical as his electoral prospects sink.

As a result, we’re finally seeing some prominent Republicans not just refusing to endorse Mr. Trump, but actually declaring their support for Mrs. Clinton. So how should she respond?

The obvious answer, you might think, is that she should keep doing what she is doing — emphasizing how unfit her rival is for office, letting her allies point out her own qualifications and continuing to advocate a moderately center-left policy agenda that is largely a continuation of President Obama’s.

But at least some commentators are calling on her to do something very different — to make a right turn, moving the Democratic agenda toward the preferences of those fleeing the sinking Republican ship. The idea, I guess, is to offer to create an American version of a European-style grand coalition of the center-left and the center-right.

I don’t think there’s much prospect that Mrs. Clinton will actually do that. But if by any chance she and those around her are tempted to take this recommendation seriously: Don’t.

First of all, let’s be clear about what she’s running on. It’s an unabashedly progressive program, but hardly extreme. We’re talking about higher taxes on high incomes, but nowhere near as high as those taxes were for a generation after World War II; expanded social programs, but nothing close to those of European welfare states; stronger financial regulation and more action on climate change, but aren’t the cases for both overwhelming?

And no, the program doesn’t need to be more “pro-growth.”

There’s absolutely no evidence that tax cuts for the rich and radical deregulation, which is what right-wingers mean when they talk about pro-growth policies, actually work, or that strengthening the social safety net does any harm. Bill Clinton presided over a bigger boom than Ronald Reagan; the Obama years have seen much more private job creation than the Bush era, even before the crash, with job growth actually accelerating after taxes went up and Obamacare went into effect.

It’s true that there are things we could do to boost the U.S. economy. The most important of these things, however, would be to take advantage of very low government borrowing costs to greatly expand public investment — which is something progressives support but conservatives oppose. So enough already with the notion that being on the center-left somehow means being anti-growth.

Now let’s talk about the politics.

The Trumpification of the G.O.P. didn’t come out of nowhere. On the contrary, it was the natural outcome of a cynical strategy: long ago, conservatives decided to harness racial resentment to sell right-wing economic policies to working-class whites, especially in the South.

This strategy brought many electoral victories, but always at the risk that the racial resentment would run out of control, leaving the economic conservatives — whose ideas never had much popular support — stranded. And that is what has just happened.

So now the strategy that rightists had used to sell policies that were neither popular nor successful has blown up in their faces. And the Democratic response should be to adopt some of those policies? Say what?

Also, I can’t help but notice a curious pattern in the recommendations of some self-proclaimed centrists. When Republicans were in the ascendant, centrists urged Democrats to adapt by moving right. Now that Republicans are in trouble, with some feeling that they have no choice except to vote Democratic, these same centrists are urging Democrats to … adapt by moving right. Funny how that works.

Back to the main theme: Grand coalitions do sometimes have a place in politics, as a response to crises that are neither party’s fault — external threats to national security, economic disaster. But that’s not what is happening here. Trumpism is basically a creation of the modern conservative movement, which used coded appeals to prejudice to make political gains, then found itself unable to rein in a candidate who skipped the coding.

If some conservatives find this too much and bolt the party, good for them, and they should be welcomed into the coalition of the sane. But they can’t expect policy concessions in return. When Dr. Frankenstein finally realizes that he has created a monster, he doesn’t get a reward. Mrs. Clinton and her party should stay the course.