Traffic moves along the Strip as members of the National Nurses United union hold LED signs to show their support for Democratic presidential candidate Sen. Bernie Sanders, I-Vt., Wednesday, Feb. 17, 2016, in Las Vegas. (AP Photo/Jae C. Hong) (Jae C. Hong/AP)

A key sign of the Republican Party’s dysfunction in recent years has been its unwillingness to produce serious policy proposals. Instead, its leading lights routinely present outlandish plans that they know can never be enacted or in which the math simply doesn’t add up.

What will Republicans do this year if elected to the White House? All GOP candidates would repeal Obamacare, some would pass a constitutional amendment to balance the budget and others would deport several million undocumented workers. Needless to say, none of this will actually happen.

Take their tax plans. The nonpartisan Tax Policy Center estimates that Marco Rubio’s would produce deficits of $8.2 trillion over the next 10 years. Ted Cruz’s plan clocks in at $10.2 trillion in deficits. And Donald Trump, predictably, outdoes them all with a proposal that would add $11.2 trillion in deficits and increase the national debt by nearly 80 percent of gross domestic product over the next two decades.

Even House Speaker Paul Ryan, famous for his budgetary expertise and pragmatism, proposed a budget in 2014 in which the math was unworkable. He promised to cut $5.1 trillion in spending over a decade — a 29 percent drop in the budget. To put this in perspective, the largest spending drop in six decades was a one-year fall of 3.4 percent, in 1955, as part of the demobilization after the Korean War.

So why do Republicans do it? Because they know what the base wants to hear, are aware that none of it is remotely plausible and so have decided that policy proposals are no longer, well, actual policy proposals. Instead, they serve as signals — emotional impulses meant to energize supporters.

The fact that none of the proposals ever gets implemented is, of course, why the conservative base is so enraged (and flocks to Cruz). In New Hampshire exit polls, half of Republican voters said they felt betrayed by their party. Moreover, the practice of using public policy as red meat has greatly contributed to the coarsening of American politics, creating an atmosphere in which crazy ideas flourish, facts are irrelevant and candidates can make absurd claims that are simply false.

The Democrats since Bill Clinton have, by and large, avoided this path. They have buttressed their policy with real data. The proposals put forward by Bill Clinton, Al Gore, John Kerry and Barack Obama as candidates were based on evidence, and the math mostly added up. Sure, their plans often contained rosy assumptions about growth and inflation, but to a far lesser extent than Republicans’ proposals. After being seen as profligate taxers and spenders in the 1960s and ’70s, the Democratic Party has convinced many centrist voters that it is the responsible party of governance.

Enter Bernie Sanders, who makes the Republicans look like models of sobriety and scholarly exactitude. The proposals listed on his campaign website add up to around $18 trillion to $20 trillion over the next decade, according to the New York Times. Adding a higher estimate on the health plan from Kenneth Thorpe of Emory University brings the total cost to more than $30 trillion.

This week, four respected economists who served Democratic presidents wrote a letter bluntly pointing out that “no credible economic research” supports Sanders’s economic assumptions and predictions. They were referring to the claims by Gerald Friedman, an economist who has tried to make Sanders’s math work. To do so, Friedman assumes that per capita growth would average 4.5 percent (more than double the rate over the past three decades), and that the employment-to-population ratio would suddenly reverse its long decline and reach 65 percent, the highest ever. Even more magically, productivity growth would rise to 3.18 percent. As Kevin Drum has pointed out in Mother Jones, “there has never been a 10-year period since World War II in which productivity grew by 3.18 percent.”

Sanders’s supporters argue that all this criticism misses the point. Sanders is setting forth an “idealistic” vision on purpose — his goal is to shift the spectrum. But that argument is premised on the notion that, in fact, the United States would be better off with $30 trillion of extra spending, absolutely free public colleges (and thus essentially government-controlled), high tariffs and top marginal tax rates of about 85 percent. It wouldn’t. Even unabashedly liberal scholars don’t believe that the economy would function better under these circumstances.

But this is nitpicking. He is painting with a broader brush, being an authentic man who speaks his mind, willing to present bold ideas geared to capture the imagination. Never mind that establishment elites criticize them as unworkable or divisive or radical.

Am I speaking about Bernie Sanders — or Donald Trump?

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