To judge by what they say and do, Democrats are obsessed with two topics: impeachment and race. With Robert Mueller’s disastrous performance driving a stake through the heart of the former, race is shaping up as a defining issue in this week’s second round of presidential debates.

As a New York Times article put it, “The searing fight over race, inequality and history has come to dominate the Democratic presidential contest.” Count that as an understatement.

Just ask Joe Biden, who’s still wondering what hit him at the first debate. But he shouldn’t get lost looking back because the same club is about to whack him again.

Hoping to copy Sen. Kamala Harris, who scorched Biden over his opposition to school busing nearly 50 years ago and leapfrogged into the top tier of candidates, Sen. Cory Booker is preparing his own assault along racial lines.

Booker, polling at a measly 2 percent, is faulting Biden’s criminal justice plan and calling him the “proud architect” of a system that led to mass incarceration of minorities. And that’s just for warmups.

“It is easy to call Donald Trump a racist now, you get no badge of courage for that,” Booker said in a preview of his debate plan before the National Urban League. “The question is, what were you doing to address structural inequality and institutional racism throughout your life? Don’t just tell us what you’re going to do. Tell us what you’ve already done.”

The logic of Booker’s plan is obvious. Beyond how it lifted Harris in the polls, her attack revealed the liabilities of Biden’s record and weak debating skills. He was shocked by her broadside and, ­unable to give a coherent answer, aimed to escape by looking at the clock and declaring in defeat, “My time is up.”

To make his predicament even starker, Biden is scheduled to stand between Harris and Booker on a Detroit stage this week.

Biden’s mental freeze in the first debate is not surprising because the 76-year-old front-runner probably assumed he was inoculated on racial issues by his faithful service as vice president to Barack Obama, America’s first black president.

But the attacks on Biden illustrate how much Dems have changed in three years. The Obama administration was the most leftist in modern times, but those days look almost modest by comparison to this year’s hysterical calls for impeaching President Trump along with overt demands for socialist and race-themed policies.

Many candidates, congressional members and activists have become shockingly radicalized. They routinely say things and advance ideas that, not long ago, were hard to spot even on the fringe. Consider that San Francisco wants to paint over a George Washington mural!

As David Brooks points out in his latest Times column, the audience for this far-far-left appeal is largely white progressives. Studies show there are more of them in the party and they moved further and faster to the left than black or Hispanic Dems.

One result, he writes, is that they see everything from immigration to the Israeli-Palestinian conflict through the prism of race.

“White liberals have warmer attitudes toward other races than they do toward their own,” Brooks ­insists.

The bizarre trend helps explain why attacks on “white privilege” are now required for candidates to prove their racial bona fides. An extreme example involves Beto O’Rourke, a wealthy white candidate from Texas who made his case for reparations by declaring that he and his wife are the descendants of slave owners. Even Senate Minority Leader Chuck Schumer, who used to claim he was a moderate, now says he will support a Booker bill to study how reparations for slavery could be put into practice.

While all this sounds like an ­exclusive appeal to minority voters, it is also just as likely to be aimed at those whites embarrassed by their race.

Of course, it is also a reaction to Trump, as is everything in politics these days. With apologies to Reggie Jackson, Trump is the straw that stirs the drink.

Where you stand on him is the key organizing principle of our time. If he is for it and you are against him, you must be against his policies even if you previously supported them.

Or, more accurately, you must be for the polar opposite of his policies.

Because he is for border control, Dems now support open borders and sanctuary cities.

Because his initial appeal was largely to white working-class voters who felt betrayed by both parties, and because he sometimes inflames racial matters, the left moves so sharply in the opposite direction that some of their ideas sound anti-white.

The increased frequency with which the “racist” tag is thrown around is one manifestation, with Rep. Alexandria Ocasio-Cortez suggesting that even Speaker Nancy Pelosi is guilty. Another is that Rep. Ilhan Omar can give an interview where she says that America should be more fearful of “white men” than Islamic terrorism — and the left defends her as being misunderstood.

Indeed, as I wrote last week, the Mueller hearing was the latest ­example of how hatred of Trump leads his enemies to do really stupid stuff. Fixated on showing they are morally superior, they swing so far to make their case that they seem to be on another planet. They even want to undo economic polices that have created record-low unemployment for black and Hispanic Americans.

Having gone to foolish extremes with Mueller and impeachment, they are now ready to repeat the mistake with race.

Road to verbosity

Contrary to the belief that the late Robert Moses never met a highway he didn’t like, there was at least one project the master New York builder opposed. It was Westway, a 1970s idea that would have sunk the West Side Highway underground for a park and development.

Moses expressed his opposition in dazzling form. Here, from a 1984 Washington Post article, is how he described Westway in 1974. Enjoy!

“I am for public works and for government aid within reason, but my imagination is staggered,” he wrote.

“How much longer can such a shindig go on? Five years? Ten years? This is not orderly consideration. It is a mob dividing up stage money, an Anvil Chorus, a byword, a hissing and a yapping, a spectacle of bamboozlement. If this is the road to progress, I am the retired Gaekwar of Baroda.”

Self-defeating art of the zeal

The resignation of a trustee of the Whitney Museum of American Art is a victory for the mob — and a defeat for art.

Warren Kanders gave more than $10 million to the museum, but some artists and staff members protested his presence on the board because his firm, Safariland, produces tear gas used by American agents on the southern border.

The protesters’ celebration will no doubt end when they chase away all the wealthy patrons who subsidize them. Which, at this rate, won’t be far off.