Former Maryland congressman John Delaney was on the receiving end Tuesday night of the most memorable slapdown of the first night of the Democratic debate in Detroit.

It came from Sen. Elizabeth Warren (D-Mass.) after Delaney had spent much of the night trying to make the case that the proposals from the two leading liberals onstage — Warren and Sen. Bernie Sanders (I-Vt.) — are unrealistic.

“You know, I don’t understand why anybody goes to all the trouble of running for president of the United States just to talk about what we really can’t do and shouldn’t fight for,” Warren said. “I don’t get it.”

Delaney didn’t get a chance to respond on Tuesday night, but he did so Wednesday morning during an appearance on Fox News — a network that Warren has characterized as “a hate-for-profit racket that gives a megaphone to racists and conspiracists.”

Presented with a clip of Warren’s line from the night before, Delaney shot back: “That’s the response when someone really can’t defend their plans,” he said.

“It’s a dishonest, kind of lazy response,” Delaney continued.

Delaney, who has struggled to get traction in the Democratic race, said Warren’s response was indicative of what’s wrong with “the extreme left of the party.”

“When I point out that the things she’s proposing are either impossible promises or fairy-tale economics, she says, ‘Oh, you’re not being ambitious enough,’” he said. “I think it’s just kind of lazy and a dishonest response.”

In recent weeks, Delaney has repeatedly criticized Warren and Sanders for embracing a single-payer health-care system, among other things.

In May, Warren announced that she had turned down an invitation to appear at a presidential town hall meeting hosted by Fox News, an opportunity some of her opponents, including Sanders, had welcomed.

At the time, Warren said the network was “designed to turn us against each other.”

During Delaney’s interview Wednesday on “Fox & Friends,” co-host Ainsley Earhardt praised the former congressman for sounding “practical” during the debate.

“We all knew that kid in school that beat you when you were running for student body president who promised to put snack machines in all the classes,” she said, alluding to Warren. “You know that’s not going to happen, but the kids hear that, and they vote for that person.”