Although Donald Trump’s presidency has not yet been catastrophic, there has always been much potential danger from the ill-informed and mercurial chief executive.

Although most economists would have problems with strangling much-needed immigration, starting a trade war with China and other nations, and cutting taxes but increasing spending, no matter whether the economy already was growing well or not (a fine tradition for every Republican president, except George H. W. Bush, going back to Richard Nixon), Trump laudably has made noises about reducing the number of troops in some of the many U.S. war zones overseas.

Yet the real danger of the Trump presidency—his tendency toward an authoritarian abuse of power—was recently apparent in his threat to declare a national emergency and have the U.S. military build the border wall, despite the House of Representatives’ refusal to give him money for it.

Since World War II, the American presidency has become too powerful compared to the original plan laid out in the Constitution by the nation’s founders, and other recent presidents have used the unconstitutional “I must act, because Congress won’t” argument—Obama did so by an executive order protecting DACA kids—but Trump has engaged in other autocratic bluster that seems to make his threat of national emergency even scarier.

For example, Trump has repeatedly bashed the news media, even threatening to pull NBC’s nonexistent “license” and employing the Stalinist phrase “enemy of the people” against them.

He has also threatened to prosecute opponents, such as Hillary Clinton and former FBI Director James Comey, and has purged law enforcement personnel who were investigating him.

Finally, he seems to have committed obstruction of justice and witness tampering by such firings and public statements to and the dangling of self-serving pardons to indicted persons connected to the investigation of Russian election tampering.

So when Donald Trump threatens to declare a bogus national emergency to allow the military to build his wall, using Defense Department money and “military eminent domain” (essentially the seizing of private land by the military), even Republicans in Congress and Trump supporters need to finally begin worrying about the potential for executive tyranny.

First, despite past presidents declaring national emergencies, the Constitution does not authorize any such government seizure of power, because the nation’s founders had had quite enough of the British military occupation in colonial America and never wanted something similar to happen again.

The Constitution only authorizes the suspension of habeas corpus (an individual’s ability to challenge detention by the government) in times of war or insurrection—and then implicitly only by Congress (because the provision is in Article I, which governs Congress’s, not the executive’s, activities). With the experience of the tyranny of the British king, the founders were unlikely to have wanted the president to be able to suspend habeas corpus (although some past presidents have unconstitutionally done so), much less go further and declare a state of emergency or impose martial law.

Second, the Constitution requires that if federal activities are undertaken, they can do so only with money appropriated by Congress. A president unilaterally reprogramming money appropriated by the Congress for use by the Defense Department to build a useless border wall is contrary to this constitutional provision.

The entire government shutdown controversy is over the House of Representatives’ refusal to fund this boondoggle. The wall is likely to cost way over the estimated $25 billion, of which Trump and the Democrats are currently fighting over the $5 billion starter money, and be ineffectual in stanching entry illegal entrants, the numbers of which, until the uptick in the last few months because of unusually dangerous conditions in Central America, had been declining for many years.

Moreover, most drugs and bad guys come right through ports of entry, not across barren desert or other terrain that an expensive border wall would need to traverse. Any desperate and determined immigrants coming across the border in these places would likely go over, under or around any wall anyway. Lastly, the biggest problem in immigration is not border crossing in remote areas; half to two-thirds of illegal immigration is people overstaying legally granted visas, which a wall does nothing about.

Finally, Republicans should be concerned about military confiscation of private land on the border to build the wall. Using “military eminent domain” is something King George would have liked. Even though Trump often likes to bluster for purposes of negotiation and to appear to be fighting for his political base (about the only thing the wall is good for), the president needs to learn that authoritarian-sounding rhetoric does matter and will quickly learn that any tyrannical bogus state of emergency in America is not likely to be tolerated.