The race to the left among the Democrats currently running for president reached a tipping point at the Detroit debate Tuesday night. The progressives and socialists of the field, Bernie Sanders and Elizabeth Warren, didn’t just behave as though their policy proposals totally blowing up and overhauling everything from healthcare to finance were three-foot putts that moderate Democrats were just too weak-kneed to attempt. They actually dismiss the moderates’ objections as “Republican talking points.”

When former congressman John Delaney, objecting to progressive proposals of single-payer “Medicare for All,” argued that many Americans were leery of the idea of losing their private insurance, Warren dismissed him out of hand, saying that “We should stop using Republican talking points” when discussing how to provide adequate health care for Americans. When moderator Jake Tapper mentioned that M4A would increase taxes on the middle class, Sanders laid into him with an accusation of bad faith: “Jake, your question is a Republican talking point . . . The health care industry will be advertising tonight on this program; they will be advertising with that talking point.”

This sort of thing is silly on its face: Just because Republicans have made an argument doesn’t mean a candidate is absolved from addressing it. Whoever wins the 2020 nomination will be forced to defend these same policies in conversation with a very pushy Republican; you’d think the least they could do is get some practice in now.

But begging off questions about their proposals isn’t just bad strategy—it also reveals something unsavory about in their “let’s move America in a totally new direction” pitch.

Progressives running on a platform of wrenching America in a dramatically socialist direction have two options in how they make their case to the public. The first is that they can engage clearly with the pros and cons of their proposals, attempting to explain clearly why arguments raised against those proposals are misguided or mistaken—or why, on balance their proposals will be a net good. Or they can pretend what they’re proposing isn’t all that dramatic or difficult, that they’re all just common-sense reforms that any fool can see will be an across-the-board improvement—and that anyone who thinks otherwise is just pushing disingenuous right-wing grumpery.

The question of Medicare for All and taxes is the perfect test case for this, because most leftist policy types don’t deny the utterly transparent fact that increased taxes—including on the middle class—are a necessary component of universal single-payer health care.

Where Americans stand to gain, Sanders and Warren argue, is by offsetting those increased taxes because people no longer having to pay insurance premiums to rapacious, for-profit companies. Making this distinction—that a myopic focus on taxes rather than total expenditures is misleading—is a critical part of the Medicare for All pitch, and many of its proponents don’t shy away from it: “Rather than paying premiums, deductibles, and copays for health care,” M4A wonk Matt Bruenig has written, “people will instead pay a tax that is, on average, a bit less than they currently pay into the healthcare system and, for those on lower incomes, a lot less.”

Now, is this argument accurate? Well, that’s another question: Mammoth, visionary expansions of government power do have a habit of never quite living up to the glowing expectations they’re supposed to achieve. But at least that’s the argument, and it’s an argument Bernie and Warren and the rest of the Medicare-for-allers are going to have to make.

Warren at least brushed up against it on Tuesday—declining to answer whether taxes would go up, but insisting that, under Medicare for all, total healthcare costs would go down. That sort of deflection isn’t going to cut it, but at least it was better than we got from others, like Beto, who just went with flatly insane pie-in-the-sky rhetoric: “The middle class will not pay more in taxes in order to ensure that every American is guaranteed world-class health care.” Paying less for a better product without implementing real structural change? Nice!

Dealing forthrightly with real concerns about your policy plans is a strategy that appeals to pols who think they’re offering an attractive project that will help everyday Americans and thus think they can win those Americans’ support honestly. Trying to pull the wool over their eyes about questions as basic as “will my taxes go up” is the strategy of choice for those who think Americans are too dumb to know their own self-interest and must thus be duped into supporting it. If the economic progressives currently running for president actually want America to line up behind their agenda, they’re much better off opting for the former. They may find voters are better at smelling a rat than they think.