Among the central elements of the U.S. Constitution are checks and balances, achieved through separation of powers. The idea, James Madison wrote, is that "ambition must be made to counteract ambition."
By design, Congress is a restraint on the president. The president has tools to contain Congress. The Supreme Court, whose members are chosen by the other two branches, has the last word on what they do.
"In framing a government which is to be administered by men over men," explained Madison, "the great difficulty lies in this: you must first enable the government to control the governed; and in the next place oblige it to control itself."
The scheme is the source of chronic frustration born of stalemate. Presidents fail to keep their promises because Congress rebels. Congress can't enact its agenda because it lacks the votes to override vetoes. And even if they can agree on what to do, their plans may die in the Supreme Court.
The beauty of a parliamentary system is efficiency. If you elect a party that promises to take some action, you can bet the action will be taken. The prospect of getting what you vote for concentrates the mind on what you really want.
Our system encourages voters to be less careful, because winning candidates often fall short of their proclaimed intentions. Barack Obama's 2009 stimulus package had to be smaller than liberal economists urged so it could pass. He got health care reform, only to see the Supreme Court invalidate significant portions. In 2008, his supporters voted for "hope and change," but the ensuing change was glacial and dispiriting.
Things will be different for President Trump. His party controls both houses of Congress, and he will get to restore the Supreme Court's Republican-appointed majority. The constitutional checks will be largely irrelevant. Trump and his party will be free to do what they campaigned on. Voters who didn't take their plans literally may be surprised when they come to pass.
A trade war is imminent because Trump has vowed to scrap the Trans-Pacific Partnership, signed by Obama, while threatening to levy a 45 percent tariff on Chinese goods and abandon NAFTA. Obamacare will be history. The nuclear deal with Iran is a dead letter.
Construction will start on a border wall with Mexico, and the government will step up efforts to deport undocumented immigrants. Tax cuts to boost economic growth will become law.
His supporters may cheer each achievement. But they may not be so pleased when they go to Wal-Mart or Home Depot and find that Trump's tariffs have raised the price of everything from clothing to power tools.
He tweeted that instead of Obamacare, "we will have MUCH less expensive and MUCH better healthcare." Some of his supporters may miss the Affordable Care Act when they lose their coverage. What will they think when they have to pay more for something they like less?
How will Trump's followers feel when Iran resumes the nuclear weapons program that Obama's deal halted -- or if the United States and Israel launch a war against Iran in response?
What will they say when Mexico refuses to pay for that wall? Or when it turns out that, as an editorial in The Wall Street Journal noted, deporting all the undocumented foreigners "would demand the departure, on average, of 84 buses and 47 chartered flights every day for two years" -- which isn't going to happen?
Trump can promise 4 percent annual GDP growth year in and year out, but he has no clue how to produce it. Trump supporters dismayed by the huge increase in the federal debt since 2008 should brace for an even bigger one under him.
If Trump's plans lead to failure or disaster, he and the Republican Party will own the results. And the voters who put their faith in him will have no one to blame but themselves.
They may come to understand the wisdom of Oscar Wilde. "There are only two tragedies in life," he wrote. "One is not getting what one wants, and the other is getting it."