Donald J. Trump may project the notion that he is a man with all the answers, but in truth he may go down in history as the man who posed many of the important questions.

No public official in modern times has challenged so many of the broad assumptions of American civic life, undermined so many of the canons of politics, recast so many of the conventions of public behavior. In a mere 18 months — to the consternation of establishment politicians, the news media and many of the special-interest groups that have controlled the conversation of the capital — he has upended the American political system. And while his rivals abhor him and scholars may condemn him, history may well applaud him for raising vital questions about American political culture, including:

• Is a permanent Washington establishment an asset in American life?

Commentators may compare Mr. Trump to outsider presidents such as Ronald Reagan, Jimmy Carter, and — the president’s favorite predecessor — Andrew Jackson, but there never has been an outsider chief executive remotely like Mr. Trump. Messrs. Reagan and Carter were governors and Jackson was a House member, the military governor of Florida and a senator before entering the White House in 1829. Mr. Trump was a businessman.

Mr. Trump’s predecessor outsiders roiled the Washington establishment, Jackson as the advance guard of a new democratic class, Carter as the head of a government of Georgians with so few ties to establishment Washington that he and his lieutenants were mocked as rubes and dismissed as amateurs, and Reagan as the representative of a glittery group of nouveau-riches contemptuous of the byways of Washington bureaucrats, liberals and the cave dwellers who ruled the capital’s after-hours social life.

 But while all three may have shifted the rhythms of Washington, they still generally conformed to the norms of politics. Indeed, the real outsiders in American politics who won major-party nominations — the businessman Wendell Willkie (1940), the jurist Alton B. Parker (1904) and the newspaper editor Horace Greeley (1872), who served a mere three months in Congress — never made it to the presidency.

But in running as a pure outsider and then governing as one, Mr. Trump is asserting that the ways of the Washington establishment are the problem, not the means to the answer. In a way, he is taking one of the less-remembered sentences from the Checkers speech of Richard Nixon — himself a senator and former House member at the time — and applying it to the entire Washington cast: “You wouldn’t trust the man who made the mess to clean it up,” Nixon said of Harry Truman and capital Democrats while pleading to remain on the 1952 Republican ticket.

• Is business acumen applicable to the political arts?

This question never has been answered at the presidential level, though it was raised briefly by Willkie three-quarters of a century ago and later by Lee Iacocca, the automobile chief who contemplated a presidential campaign himself.

 But the precepts of business and the folkways of politics are rarely compatible. Business executives compete for market share, so even if Pepsi doesn’t outperform Coke, there are plenty of profits for Pepsi — and even some left over for RC Cola. Coming close in an election, or in any upcoming Senate vote on health care, gets a politician nothing but a stinging defeat.

• Why do intelligent, engaged citizens examine the same world and yet have vastly different perceptions?

Mr. Trump’s supporters see him as the eloquent spokesman for the dispossessed and left-behind while his opponents regard him as a boorish charlatan. His supporters, for example, believe he will bring back mining and manufacturing jobs to ailing rural and industrial regions, but his opponents believe that coal is swiftly receding into the past and automation is rendering a comeback of manufacturing jobs unrealistic. His supporters believe that trade agreements cost Americans jobs, but his opponents just as fervently believe the opposite. There is no middle ground and, more to the point, no common ground.

• Is there such a thing as the truth?

This is perhaps the most perplexing question raised by Mr. Trump’s time in office, when the mainstream media face questions from the White House about their veracity and fairness, not to mention questions about their financial survival.

When Kellyanne Conway, a top Trump spokeswoman, spoke of “alternative facts,” no one, almost certainly even in the White House, seriously believed that provable facts — the multiplication table, for example, or the notion that in a right triangle A squared plus B squared equals C squared — have contradictory alternatives. They do not, nor does a Trump Inauguration Day crowd clearly smaller than that of the president’s predecessor qualify as a crowd that was bigger.

But the notion of “alternative” facts raises a more fundamental question, relevant to the growing practice of Americans seeking facts, and comfort, only from news outlets that share their views. For it is possible for a news reporter to assemble facts to create a single truth while for another reporter, those facts, or other facts, can be arranged differently to produce a separate truth. The Sunday newspaper is not the place to examine this in depth, except to cite the Truman-era notion that, as veteran Washington bureaucrat Rufus E. Miles Jr. put it, “Where you stand depends on where you sit” — and to add that facts by definition are not debatable.

• Has a political party that for generations dedicated itself to serving the poor and the striving become instead the province of the educated and the elite? And, conversely, can a party that for decades has served business interests transform itself into a populist vanguard?

By running for president as a Republican and frequently campaigning with rhetoric borrowed from the Democratic playbook, Mr. Trump has brought into question the entire architecture of modern American politics. Because he did so at a time when the Democrats (and their nominee, former Secretary of State Hillary Rodham Clinton) campaigned on issues congenial to urban elites and university liberals rather than the blue-collar voters FDR brought into the Democratic coalition, this is the perhaps the pre-eminent question in American civic life today. The way it is answered will shape American politics long after Mr. Trump fades from the scene.

These questions may be troubling but are overdue for examination. One, maybe two, cheers for Donald Trump for raising them. But only one for the answers both Republicans and Democrats are providing.

David M. Shribman is executive editor of the Post-Gazette (