(Tribune News Service) — It’s one of the classic lines in America cinema. In “Butch Cassidy and the Sundance Kid,” Paul Newman and Robert Redford are cornered by a posse of lawmen, and the only escape is to leap from a cliff into the river below. When Sundance says he won’t jump, because he can’t swim, Butch reassures him: “The fall will probably kill you.”

It’s a sad metaphor for U.S. foreign policy. As Donald Trump marches toward the Republican presidential nomination, it’s only natural to wonder what will happen if the U.S. is once again led by an erratic, impulsive and frequently destructive president. But speculating about Trump’s impact is like wondering what happens after a precipitous plunge.

The great crisis of U.S. foreign policy isn’t something that will materialize only if Trump wins in November. It’s happening right now, as America struggles to provide the aid an embattled Ukraine needs to survive.

On Capitol Hill, there doesn’t seem any great urgency. A vital funding resolution has been postponed, first by protracted negotiations in the Senate — on a deal combing border security with Ukraine aid — that ultimately went nowhere, then by a two-week recess the Republican-led House took after receiving the bill the Senate eventually passed, and then by the latest frenzied efforts to keep the U.S. government running for a few more weeks. As Washington dithers, the battlefield effects pile up.

The eastern city of Avdiivka fell late last month because Ukrainian forces lacked the shells and bullets needed to stop unending Russian attacks. Now, Moscow is pressing onward. Russia’s air force, which previously played a limited, unimpressive role in this war, is getting into the fight by pulverizing areas into which the Russian army can then advance. President Vladimir Putin’s planes would, of course, be very vulnerable to Ukraine’s air defenses — if Ukraine still had enough of these systems to keep the Russian air force at bay.

For Ukraine, the costs of a shortfall in U.S. aid aren’t prospective or hypothetical. They are real, and they are mounting by the day, in lives and territory lost. Put bluntly, we are seeing how Ukraine loses this war — not because of some brilliant Russian blitzkrieg, but because of the incremental accumulation of setbacks that deprive the country of any hope of victory, and thereby force it to accept a peace that is effectively a strategic defeat.

Which brings us back to U.S. policy. At the Munich Security Conference last month, and in capitals around the world, the specter of a Trump revival has been weighing on U.S. allies. And for good reason, given that Trump is doing all the same things — talking about throwing allies to the wolves, fantasizing about an assault on America’s democratic institutions — that alarmed so many U.S. friends the first time around.

But the Ukraine impasse should be even more alarming to those who depend on the U.S. for their safety. That’s because it’s hard to believe America will send its men and women to defend U.S. allies when the next crisis comes, if it won’t even send money and arms to support Ukraine in a conflict that hasn’t killed a single U.S. service member. The Ukraine impasse also shows that the rot in the U.S. political system goes deeper than the rantings of a rogue president.

Yes, Trump has played his shameful part in the Ukraine debate: His resistance to fixing America’s southern border, because he wants to run on that issue in November, helped tank the bipartisan agreement Senate dealmakers produced. His opposition to Ukraine aid is emboldening his MAGA allies, and frightening internationalist Republicans, in the House right now.

But the current debate demonstrates that the U.S. political system can be paralyzed on critical strategic issues even when America’s president has described Ukraine as the central front in a great struggle between autocracy and democracy, and when even a solid majority of House and Senate legislators favor giving that country support. If this is the best the U.S. can do under Joe Biden, it won’t take a second Trump presidency to cast America’s global role into doubt.

In a recent essay for Foreign Affairs, former Secretary of Defense Robert Gates argued that U.S. political dysfunction is abetting geopolitical instability — that a divided America lacks the constancy and commitment needed to hold back the forces of global disorder. The longer the Ukraine impasse continues, the more prescient that warning looks.

We live in an era when many longtime verities of global affairs — the advance of democracy, the absence of great-power war, the relative stability of key regions — are coming into question. So is the uber-verity that underpins all the others: That America’s political system, for all its foibles and absurdities, will eventually produce policies that nudge the world in a positive direction. Whatever happens in November, the Ukraine aid stalemate is sobering because it gives America’s friends, and its enemies, a preview of what the world will look when that’s no longer the case. It could be a very long way down.

Hal Brands is a Bloomberg Opinion columnist and the Henry Kissinger Distinguished Professor at Johns Hopkins University’s School of Advanced International Studies. This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

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