President Donald Trump, an ongoing eruption of self-refuting statements (“I’m a very stable genius” with “a very good brain”), is adding self-impeachment to his repertoire. Spiraling downward in a tightening gyre, his increasingly unhinged public performances (Google the one with Finland’s dumbfounded president looking on) are as alarming as they are embarrassing. His decision regarding Syria and the Kurds was made so flippantly that it has stirred faint flickers of thinking among Congress’ vegetative Republicans.

Because frivolousness and stupidity are neither high crimes nor misdemeanors, his decision, however contemptible because it betrays America’s Kurdish friends, is not an impeachable offense. It should, however, color the impeachment debate because it coincides with his extraordinary and impeachment-pertinent challenge to Congress’ constitutional duty to conduct oversight of the executive branch.

Aside from some rhetorical bleats, Republicans are acquiescing as Trump makes foreign policy by and for his viscera. This might, and should, complete what the Iraq War began in 2003 — the destruction of the GOP’s advantage regarding foreign policy.

Democrats were present at the creation of Cold War strategy. From Harry Truman and Dean Acheson through Sen. Henry Jackson and advisers such as Max Kampelman and Jeane Kirkpatrick, they built the diplomatic architecture (e.g., NATO) and helped to maintain the military muscle that won the war. But the party fractured over Vietnam, veering into dyspeptic interpretations of America’s history at home and abroad, and a portion of the party pioneered a revised isolationism. Conservative isolationism had said America was too virtuous for involvement in the fallen world. Progressive isolationism said America was too fallen to improve the less-fallen world.

Hence Republicans acquired a durable advantage concerning the core presidential responsibility, national security. Durable, but not indestructible, if Democrats will take the nation’s security as seriously as Trump injures it casually.

Trump’s gross and comprehensive incompetence now increasingly impinges upon the core presidential responsibility. This should, but will not, cause congressional Republicans to value their own and their institution’s dignity, and exercise its powers more vigorously than they profess fealty to Trump. He has issued a categorical refusal to supply witnesses and documents pertinent to the House investigation of whether he committed an impeachable offense regarding Ukraine. This refusal, which is analogous to an invocation of the Fifth Amendment protection against self-incrimination, justifies an inference of guilt. Worse, this refusal attacks our constitutional regime. So, the refusal is itself an impeachable offense.

In 1974, the House articles of impeachment against Richard Nixon indicted him for failing “without lawful cause or excuse to produce papers and things as directed by duly authorized subpoenas issued by” a House committee, and for having “interposed the powers of the presidency against the lawful subpoenas” of the House.

If Trump gets away with his blanket noncompliance, the Constitution’s impeachment provision, as it concerns presidents, will be effectively repealed, and future presidential corruption will be largely immunized against punishment.

In Federalist 51, James Madison anticipated a wholesome rivalry and constructive tension between the government’s two political branches: “Ambition must be made to counteract ambition. The interest of the man must be connected to the constitutional rights of the place.” Equilibrium between the branches depends on “supplying, by opposite and rival interests, the defect of better motives.” But equilibrium has vanished as members of Congress think entirely as party operatives and not at all as institutionalists.

Trump is not just aggressively but lawlessly exercising the interests of his place, counting on Congress, after decades of lassitude regarding its interests, being an ineffective combatant. Trump’s argument, injected into him by subordinates who understand that absurdity is his vocation, is essentially that the Constitution’s impeachment provisions are unconstitutional.

The canine loyalty of Senate Republicans will keep Trump in office. But until he complies with House committee subpoenas, the House must not limply hope federal judges will enforce their oversight powers. Instead, the House should wield its fundamental power, that of the purse, to impose excruciating costs on executive branch noncompliance. This can be done.

In 13 months, all congressional Republicans who have not defended Congress by exercising “the constitutional rights of the place” should be defeated. If congressional Republicans continue their genuflections at Trump’s altar, the appropriate 2020 outcome will be a Republican thrashing so severe — losing the House, the Senate and the electoral votes of, say, Georgia, Arizona, North Carolina and even Texas — that even this party of slow-learning careerists might notice the hazards of tethering their careers to a downward-spiraling scofflaw.

George Will is a columnist for The Washington Post.