America’s distinctive contribution to philosophy is called pragmatism. Like all notions that have been marinated and masticated by generations of academic philosophers, this movement has been minced to bits. At the beginning, though, in the late 19th and early 20th centuries, pragmatism was a reaction by the likes of C.S. Peirce , William James and John Dewey to the idealistic philosophies of Europe. Truth is not to be found in some palace of the mind apart from the world, they argued. Rather, the truth of an idea is measurable by its effects.

Well, duh, you might say. And that’s sort of the point: All great and true philosophies eventually seem self-evident after enough experience. Pragmatism advanced largely because its alternative — analytical idealism — has been such a grotesque practical failure. Over the past century, grand theories of racial supremacy, nationalist destiny and communist utopia were repudiated by their terrible real-life effects. Even the more recent notion that the whole world hungers for American-style democracy has run aground on the reef of reality.

Most Americans aren’t philosophers, thank goodness, but we are a nation of pragmatists. And so, despite the snap to her zinger, Sen. Elizabeth Warren (Mass.) was out of the mainstream when she shrugged off criticism during the second round of Democratic debates by saying: “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.”

An American president ought to care deeply about the effects of her ideas — whether she can actually do the things she promises and whether her idealistic “should-dos” are also pragmatic “could-dos.” Former congressman John Delaney (Md.) was hardly out of place at a forum of would-be presidents when he expressed practical concern that hospitals can’t survive if all their services are reimbursed at Medicare rates, as Warren proposes to do.

(The hunt for evidence on this question might include a look at Canada, the favorite health-care Shangri-La of Warren’s fellow idealist Sen. Bernie Sanders (I-Vt.). Hospitals up north are chronically underfunded under the government-run, single-payer system. Here’s the spokesman for the Hospital for Sick Children, which is known in Canada as SickKids: “SickKids can’t be responsible for the full cost over the course of treatment of a child that’s going through a complicated disease.”)

Asking what works is an essential element of the Progressive tradition. Reformers of the early 20th century steeped themselves in data and tested their theories relentlessly in the laboratory of the streets. In 1910, a young Frances Perkins personally inspected more than 100 New York bakeries before proposing new sanitation laws.

The original Progressives were incrementalists and compromisers. They built coalitions by offering — and then delivering — concrete results.

Pragmatism has never been more urgently needed in American politics. The widespread loss of faith in government reflects a half-century of overpromising by politicians with Big Ideas. The war in Vietnam was an insufficiently challenged Big Idea, as was the war in Iraq. Globalization was going to enrich all Americans. The Internet would be a source of unalloyed good. Tax cuts were going to trickle down.

President Trump is the direct beneficiary of that loss of faith. But the answer to Trumpism is not a demagoguery of the left. If Democrats hope to persuade Middle America that facts matter, they can’t hide behind emotional appeals to unvetted notions.

Democrats should be demanding more answers, not fewer. Will Medicare-for-all cost key union votes in critical Midwestern states, as Rep. Tim Ryan (D-Ohio) argued during the debates? Does a free-tuition promise at state colleges and universities benefit middle- and upper-class families more than families in need? Is Warren’s proposed tax on the assets of wealthy Americans likely to pass constitutional muster, and what strategies are billionaires likely to employ to avoid it? In light of those answers, will it really pay for all that she has promised?

Do Americans support decriminalizing illegal border crossings? Do Americans oppose lawful deportations? Do Americans agree that the federal government should guarantee a job for every person? Pragmatic questions such as these are highly relevant in a representative democracy, where politics is the art of the possible.

What I don’t understand is why anybody goes to all the trouble of running for president of the United States simply to ignore questions about real-world realities and promise fights without explaining how to win them. Reality is not going to bend to a new shape come 2021 just because a President Sanders shouts at it or a President Warren fights with it.

On the other hand, if their ideas are sound and their promises are true, there’s no better way to demonstrate that than through diligent testing and vigorous challenges. Contrary to what we heard again and again in the debates, that’s not a “Republican talking point.” It’s an American conviction.

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