Participants hold signs as Democratic U.S. presidential candidate U.S. Sen. Bernie Sanders (I-VT) speaks at a news conference to introduce the "Medicare for All Act of 2019" on Capitol Hill in Washington, U.S., April 10, 2019. REUTERS/Aaron P. Bernstein - RC17027C4EA0

Bernie Sanders introduces the “Medicare for All Act of 2019″ in Washington, D.C. on Apr. 10, 2019.

Aaron P. Bernstein/Reuters

I have a simple piece of advice for the 10 Democratic presidential candidates on stage tonight at Tyler Perry Studios in Atlanta, Georgia.

When they are inevitably asked by a moderator from MSNBC or the Washington Post how they plan to “pay for” one of their signature proposals — whether it is Medicare for All (Elizabeth Warren), a Green New Deal (Bernie Sanders), baby bonds (Cory Booker), middle-class tax cuts (Kamala Harris), or a universal basic income (Andrew Yang) — they should respond with one word: Mexico.

Mexico, they should say, with the straightest of straight faces, will pay for it.

Yes, that line would get a big laugh from the crowd in the hall. It would go viral online. It would endear the candidate who dares say it to Democratic voters watching at home (many of whom are fed up with debate moderators who constantly frame their questions around GOP talking points). It would help that candidate dominate the post-debate headlines on cable news.

But it would do much more than that: It would serve a major strategic purpose. Democrats who dare to remind pundits and the public of Donald Trump’s ridiculous yet oft-repeated campaign pledge that “Mexico will pay for the wall” would finally be drawing a crucial line in the sand and saying to Republicans, to the media, and even to each other, that they will no longer be playing the tiresome and very right-wing “pay for” game.

The reality is that voters care more about finding solutions to substantive issues than they care about deficits. A new survey conducted by pollsters YouGov for the progressive think tank Data for Progress, for example, found 51 percent of voters back spending billions of dollars on clean energy infrastructure by increasing the deficit, compared to 47 percent who back increasing taxes to pay for such spending.

Back in June, toward the very beginning of the first Democratic presidential debate in Miami, Florida, moderator Savannah Guthrie of NBC News asked Kamala Harris whether Democrats had a “responsibility to explain how will they pay” for every major proposal they make. “I hear that question, but where was that question when the Republicans and Donald Trump passed a tax bill that … benefits the top 1 percent and the biggest corporations in this country, contributing at least $1 trillion to the debt of America, which middle-class families will pay for one way or another?” the California senator responded, to loud cheers and applause from the audience inside the hall.

Frustratingly, though, other Democrats have failed to follow her lead. Instead, in recent months, establishment-friendly candidates such as Joe Biden, Pete Buttigieg, and Amy Klobuchar have fallen over one another to attack ambitious and progressive policies such as Medicare For All for being unaffordable and, ergo, unachievable. “It’s impossible to pay for Medicare for All without middle class tax increases,” declaimed Biden earlier this month, doing his best impression of a Senate Republican.

Under intense pressure from her rivals, as well as from the media, Elizabeth “I have a plan for that” Warren even released a detailed proposal explaining how she would raise $20.5 trillion to fund her version of Medicare for All. She gained little more than attacks from her left and from her right, not to mention negative news headlines.

It’s like watching the sequel to a truly awful movie. In 2016, Democratic candidate Hillary Clinton produced a plethora of very comprehensive and carefully costed plans and policies, earning the sobriquet of “Wonk in Chief” in the process.

Trump, on the other hand, ranted about an “impenetrable$21 billion wall on the southern border and declared more than 200 times during the campaign that Mexico would pay for it.

In fact, Trump not only guaranteed that Mexico would fund his racist barrier — “They may even write us a check,” he told Fox News’s Sean Hannity — but he also promised to eliminate the $19 trillion national debt over eight years. (It has, in fact, increased by almost $4 trillion in his first three years in office.)

Some might say Trump was mocked for making such “grandiose” pledges, to borrow a line from the New York Times. But did all the Twitter snark stop him from entering the Oval Office? And has he ever been held to account by an interviewer on why he repeatedly lied about how Mexico would pay for his beloved border wall?

From where I’m sitting, Trump got away with it. And he’ll get away with it again in 2020 because Republicans don’t care about deficits — or details. Only Democrats do. And only Democrats are expected to.

In this Trump era, journalists have been rightly lambasted for their lazy “both sides” coverage of issues such as brazen racism, open corruption, and serial dishonesty. When it comes to the “pay for” debate, however, it’s even worse: there is no “both sides-ism.” It’s only the Democratic side that is expected to account for where it will get every dollar and cent to pay for every single policy that they unveil. Republicans, as Harris pointed out, get a pass. It’s not just Trump’s tax cuts or his border wall: When was the Trump administration asked how it is paying for the $28 billion bailout for farmers hurt by the trade war with China? When were Republicans in Congress asked how they funded their whopping $130 billion increase in the Pentagon budget between 2015 and 2019?

A handful of Democrats are refusing to play along. Last year, Sen. Brian Schatz, D-Hawaii, offered a pretty robust response to a question from Vox about how he would fund his $95 billion proposal to offer debt-free college to students at public universities.

“I don’t play the pay-for game,” the senator replied. “I reject the pay-for game. After the Republicans did the $1.5 trillion in unpaid-for tax cuts … I just reject the idea that only progressive ideas have to be paid for. We can work on that as we go through the process, but I think it’s a trap.”

It is a trap that the Democrats’ own leader in the House, Speaker Nancy Pelosi, has set for the next Democratic president, by insisting on pay-as-you-go rules that prevent future deficit spending. “We cannot just increase the debt,” she told Bloomberg News earlier this month.

Are you kidding me? Reckless Republicans blow trillions on unfunded tax cuts, and sober Democrats are supposed to clean up the mess? And, that too, at a time of record-low interest rates?

Democrats need to stop playing by the old rules. I understand the logic of the “I have a plan for that” mantra; I get the appeal of wanting to be the adults in the room. But the man-child that the Democrats seek to defeat next year was elected to the highest office in the land in 2016 without a plan for anything.

Never forget: He said Mexico would pay for his signature issue. And he won. Now, defiant Democrats should say the same.