Standard debate practice for established politicians under challenge by a nobody is to virtually ignore them. Get your own message out and deal with the anticipated attacks as necessary, then turn back to yourself ASAP. The challenger must make the waves to get noticed.

But there’s an interesting dynamic within current Democratic Party politics that emerged in this week’s gubernatorial primary debate between two-term incumbent Andrew Cuomo and TV actress turned activist Cynthia Nixon. Right after it ended, our colleague Jazz Shaw covered the debate itself.

It was the incumbent Cuomo who came out attacking the nobody as inexperienced and unqualified, despite his mammoth purported lead in the polls. Nixon was an aggressor too, as expected.

Now, why do you suppose this is?

Recent Democrat primary experiences tell the governor to forget the polls, he could get whacked the way other establishment figures have gone down to far-left challengers playing off the growing surge of socialist sentiment in their party.

In June, the No. 4 Democrat House leader, Joe Crowley, was far ahead in the polls for a new term in New York City. Last election he wasn’t even challenged. This time he was upset in the primary by young socialist Alexandria Ocasio-Cortez. She became an instant party star.

This week in Florida’s Democratic gubernatorial primary a far-left progressive Tallahassee mayor, Andrew Gillum, surged from nowhere to upset the establishment’s candidate Gwen Graham, daughter of the former senator and governor.

That set up what augurs to be an epic struggle of surrogates there leading up to the Nov. 6 vote-counting. Gillum, backed by Bernie Sanders, the socialist-sometimes-pretend-Democrat-when-it’s-convenient senator, and the Republican nominee, Rep. Ron De Santis, who is strongly backed by President Trump.

You could argue Hillary Clinton took Wisconsin and Michigan for granted in 2016, to her electoral vote regret. And her party has long taken black and Latino voters for granted.

The lesson from all this for New York’s Cuomo is: Do not take your large lead for granted. In their debate Wednesday night Cuomo came out charging and so did Nixon. They ended up talking over each other and accusing the other of lying.

She accused the Cuomo administration of “incredible corruption.”

“I’m not an Albany insider like Governor Cuomo,” a poised Nixon charged in her first political debate, “but experience doesn’t mean that much if you’re not actually good at governing.”

Cuomo described the actress as inexperienced and warned her that in government you don’t just snap your fingers to get something done. Cuomo did make some news by categorically vowing to serve a full term, if reelected, and not run for president in 2020.

The governor, who’s taken flak for saying recently that America never was that great anyway, sought to don the mantle of Trump fighter. “No one has stood up to Donald Trump the way I have,” he claimed.

This year New York’s primaries are scheduled for a Thursday, Sept. 13, to avoid conflicts with the 9/11 anniversary and the end of Rosh Hashanah, the Jewish New Year.