(CNN) "We're going into the war with some socialists," President Donald Trump told an adoring audience of Republican congressmen this week, sharing his assessment of the coming election and saying he had a new theme for his campaign.

"I love the idea of 'Keep America Great' because you know what it says is we've made it great now we're going to keep it great because the socialists will destroy it."

Saving the country from fears he's stoking about socialism has become his main strategy to demonize Democrats, and he's seized on the rise of self-described democratic socialists like Bernie Sanders, the independent Vermont senator running for president as a Democrat, and Alexandria Ocasio-Cortez, the new congresswoman who introduced the Green New Deal.

Other Democrats, from Sen. Elizabeth Warren to Former US Rep. Beto O'Rourke have made clear they're not socialists, but capitalists with caveats . There's something to Trump's attacks. In a recent NBC News / Wall Street Journal poll , 50% of US adults said they viewed socialism either somewhat or very negatively compared to just 18% who said they had a positive view of socialism. Just 25% of people in that poll said they'd be enthusiastic about or comfortable with a socialist presidential candidate while 72% said they would be uncomfortable or have some reservations with a socialist presidential candidate. That was the least popular candidate attribute tested, although there were clear reservations about a candidate over the age of 75.

South Bend, Indiana, Mayor Pete Buttigieg pushes what he calls democratic capitalism and argues the country is actually to the left of Congress and the Democratic Party on everything from gun laws to health care. He said Thursday on Good Morning America that Trump's strategy won't work.

Buttigieg was asked by George Stephanopoulos about an essay he wrote in 2000 that won a national Profiles in Courage essay contest and whether his thoughts then were a liability now. The essay by then-high schooler Buttigieg praised Sanders, then a six-term 59-year-old lawmaker, for being a proud socialist in a time of poll-tested centrism. Buttigieg said centrism had led to cynicism among voters and that was, "perhaps, the greatest threat to the continued success of the American political system."

First, Buttigieg made clear to Stephanopoulos he wasn't necessarily applauding Sanders for his socialism.

"What I was praising Sen. Sanders for was for being honest about what he believed, and I think we need more of that," said Buttigieg.

But then Buttigieg said something interesting about Trump's attacks -- that they're worn out and from a different generation. A big part of Buttigieg's own argument is that American politics needs generational change, which is notable given the reservations voters have about candidates over the age of 75. Former Vice President Joe Biden is 76, Sanders is 77 and Trump is 72.

"The President is adopting a tactic that takes us back to the darkest days of the '50s when you could use the word 'socialist' to kill somebody's career, or to kill an idea, but that trick has been tried so many times that I think it's losing all meaning," Buttigieg said.

"The Affordable Care Act was a conservative idea that Democrats borrowed and they called that 'socialist.' So it's kind of like the boy who cried wolf. It's lost all power I think, especially for my generation of voters."

Invoking that generational difference could work to the advantage of 37-year-old Buttigieg, who was born decades after the 1950s ended.

Medicare for all and socialism

Among the Democratic proposals Trump says is socialist is Sanders' plan for Medicare for all, which would take over the private health insurance industry and replace it with a government-run system.

Medicare for all has become something of a catchphrase this year for Democrats. Most presidential candidates don't support a Sanders-style system, but all of them seem to like that phrase, Medicare for all.

Buttigieg told Stephanopoulos he supports Medicare for all, but not in the Sanders mold. He said he'd rather offer a public option and then said he thought people would choose that over the private market.

"You might call it medicare for all who want it," said Buttigieg. "You take a version of Medicare, you let anybody who wants to buy into it buy into it, and then if people like me are right that that's going to be a preferred option that very naturally becomes a kind of glide path toward a Medicare for all environment, but it also dares the corporate world to come up with a better solution than what they've done so far."

There will be no room for that level of nuance in Trump's telling (or even Sanders' for that matter).

In fact, the day after he spoke to Republicans about socialism, Trump was tweeting about health care.