Washington — So far: President Trump has announced a crisis that isn’t actually a crisis, requiring a wall that is not really a wall, funded by Mexican pesos that are really American tax dollars, to keep out murderous migrants who are (as a whole) less violent than native-born Americans, leading to congressional negotiations that involve no actual negotiations, resulting in a government shutdown undertaken on the advice of radio personalities, defended in an Oval Office address that consisted of alarmism, prejudice, falsehood and other material caught in the P-trap of Stephen Miller’s mind.

One conservative claimed that Trump finally looked “presidential.” Actually, we are seeing the federal government — Trump supporters and opponents — trying to explain and respond to an impulsive, emotive, selfish, irresponsible and fundamentally irrational force at its center. It is like the immune system responding to a virus it has never seen before and cannot defend against. Trump walks in and out of meetings, repeating scraps of his stump speech, unpredictable to his staff, unconcerned about the pressure on his allies, contemptuous toward congressional opponents and with no apparent end game except their total surrender.

This is a case study in failed and erratic leadership. The shutdown happened because Trump — under pressure from partisan media — reneged on a commitment to sign the spending bill the Senate had passed and the House was ready to pass. Then, in an Oval Office meeting with the Democratic leaders, he said he would gladly own a shutdown, presumably because he figured it would look good on TV. Trump apparently did this without talking to congressional Republicans or his own staff. Then congressional Republicans and his own staff were forced to defend Trump’s impulse as a strategy. But this has proved difficult, because Republicans have no leverage. So now the whole GOP is left pretending there is an emergency at the border, and that a multiyear construction project is somehow the best way to deal with an emergency.

This is the Republican legislator’s lot in the Trump era — trying to provide ex post facto justifications for absurd presidential choices. The border “crisis” did not break because of some tragedy caused by a porous southern border. It did not result from some serious determination of national security priorities. The whole GOP strategy and all the arguments they are using are really backfill for an intemperate choice made by a president in response to media coverage. It is a dynamic we’ve seen again and again. Trump announced a summit with Kim Jong Un because, well, for the hell of it. Then the whole government had to backfill a policy and process to fit his wrongheaded announcement. Trump announced the withdrawal of American troops from Syria on the spur of the moment, perhaps to assert himself against the influence of his now-departed Defense Secretary James Mattis. Then the whole defense and national security establishment has to scramble to backfill the details of coherent policy (which they still haven’t really done).

On the issue of border security, it has fallen to Homeland Security Secretary Kirstjen Nielsen to provide justification for the irrational. And this has turned a serious public servant into a font of deception and bad faith. She warns darkly about a terrorist threat crossing our southern border, though both the size and details of that threat are too “sensitive” to release. “I am sure all Americans,” she explains, “would agree that one terrorist reaching our borders is one too many.”

So, we know that the number of terrorists intercepted at the southern border is equal to or greater than one. What we don’t know is how this terrorist threat compares to other dangers and vulnerabilities that require funding as well. I have talked to many counterterrorism experts about domestic radicalization, and foreign intelligence gathering, and drones and special operations, and financial investigation and disruption. I have never met an expert who mentioned the construction of a physical barrier with Mexico as an urgent priority in the fight against global terrorism. Some benefit in this area may be a highly attenuated byproduct of a wall. But if the goal is fighting terrorism, the first dollar would not go to a wall. Or probably the billionth dollar. The argument is deceptive to its core.

But security arguments would certainly be at the core of Trump’s justification for declaring a national emergency and building the wall with American troops — if he makes that choice. Then the ignorance, arrogance and stubbornness of one man would turn a budget crisis into a constitutional crisis — and turn Republican defenders into abettors of creeping authoritarianism. All to justify a fool’s impulse.

— Michael Gerson is a columnist for Washington Post Writers Group.