WASHINGTON — As the United States faces the possibility of a government shutdown at month’s end, President Trump is learning the hard way the difference between demanding what he wants as a business tycoon and getting it as the chief executive in an electoral democracy of three separate and equal branches of power.

He discovered in the first weeks of his presidency how the judiciary could stop in its tracks his executive order banning travel to the United States of certain foreign nationals. Then he learned, in hurriedly trying to deliver on his campaign promise to “repeal and replace Obamacare,” that members of his own party and Democrats in the House were not going to roll over and do his bidding.

Near the end of his third month in the Oval Office, Trump is still struggling to overcome the basic public concern that he lacks the knowledge and skills to run this huge country’s domestic or foreign affairs. He has been slow to assemble a cast of competent supporting characters in his cabinet.

In a measure of the pubic apprehension, Trump’s choices of three military men, Marine Gen. James Mattis as secretary of defense, Army Lt. Gen. H.R. McMaster as national security adviser and Marine Gen. John F. Kelly as secretary of homeland security have been applauded as watchdogs against Trump’s impulsiveness.

But he has also brought into his administration a conspicuous preacher of economic nationalism in Stephen Bannon, who openly espouses the “deconstruction” of the federal bureaucracy. It signals intentional chaos, as does his selection of Scott Pruitt of Oklahoma, an open denier of climate change as a man-made phenomenon, to be administrator of Environmental Protection Agency.

In all, an aura of amateurism steadily spreads over the Trump administration, as family members have been placed in critical policy positions. The president’s daughter Ivanka and her husband, Jason Kushner, have raised serious ethical questions, as new conflicts of interest between their businesses and the nation’s business surface seemingly every day.

Meanwhile, the Republican Party establishment, so conspicuously shattered in Trump’s humiliation of the 15 also-rans in the 2016 GOP primaries, essentially stands helplessly by. The new president ignores them and sounds an uncertain policy trumpet, offering an agenda plucked from his mixed bag of campaign promises he said he would deliver in his first 100 days.

Trump readily referred to the 100-day milestone during last year’s campaign, but now he conveniently dismisses it as a meaningless measure of governing achievement.

In any event, inevitable comparisons of Trump’s first 100 days are running very unfavorably compared with ratings of earlier first-term presidents in the poll-taking era. Dwight Eisenhower had 73 percent favorability in 1953 and JFK 83 percent in 1961. The latest ABC News/Washington Post poll had Trump at 42 percent favorable, 53 percent unfavorable — the lowest negative figure on record.

Yet the core support that brought him his narrow Electoral College victory seems to be holding, even as pointed public protests against him mount. It seems likely the dysfunction and difficulties of his first three months in office will continue as the temperamental and unpredictable Donald Trump seeks a plausible presidential image that so far still eludes him.

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Jules Witcover is a nationally syndicated columnist.