Ukrainian President Volodymyr Zelenskyy visited the United Nations and the White House last week, seeking more support for his country in a war that won’t end anytime soon. Zelenskyy’s chief backer, the U.S., will need a shift in strategy to help Ukraine survive and prevail in a protracted war, even as the politics of the conflict get harder in Washington.

It may seem odd to forecast a grim, protracted struggle just as Ukrainian troops are finally opening gaps in Russia’s strong defensive lines. But barring a catastrophic collapse of Russian resistance, Ukraine won’t liberate all of its territory this year. The war may not end next year, either, given that Russian President Vladimir Putin is likely pinning his hopes for victory on the return of Donald Trump as U.S. president — and a corresponding collapse in Western unity — after November 2024. The fighting may well drag into 2025 or even longer, presenting new challenges in a new phase of the war.

Phase one of U.S. strategy, in 2022, involved giving Ukraine enough aid to avoid losing while also inflicting appalling costs on the invaders. The success of that effort led to phase two: preparing Ukraine for a counteroffensive meant to claw back territory and perhaps make peace on favorable terms. This phase has been more disappointing, due to slow progress on the battlefield -- and the fact that Putin is so committed to victory that he was always unlikely to come to terms.

Even now, the peace Putin wants would leave Ukraine indefensible and dismembered. So unless the U.S. opts for disengagement — tantamount to Ukrainian defeat — it needs to start addressing the problems a longer war will confront.

The first involves assessing, and perhaps adapting, military strategy. Ukraine’s current offensive initially struggled because the country sought to mimic Western tactics without the advantages, such as air superiority, Western militaries have come to expect.

The U.S. and its allies need to start equipping Ukraine now for operations in 2024 and after. The question is whether they should be preparing Ukraine for a similar offensive next year, or perhaps helping it employ a more familiar, if less ambitious, strategy of attrition. This would involve localized offensives combined with ramping up long-range strikes meant to sever Russia’s supply lines and gradually make its military position unsustainable.

Second, a longer war may require accepting higher risks of escalation. At the outset, Washington stepped across Putin’s red lines gingerly. More recently, the U.S. has committed to provide sophisticated capabilities such as Abrams tanks and F-16 fighter jets.

These commitments are meant to show that Putin can’t simply outwait the West. But if a new theory of victory involves coercing, rather than directly evicting, Russian forces, Ukraine will need longer-range ATACMS missiles and other systems to vastly increase the pain it inflicts by targeting Putin’s forces wherever they occupy Ukrainian soil.

Third, Washington must tighten the economic squeeze. Sanctions have injured but not crippled Putin’s economy, which continues to churn out weapons for the war. The Treasury and State departments are already cracking down on sanctions evasion, with the announcement this month of further penalties on 150 individuals and entities. The next step might be lowering the price cap the Group of 7 imposed on Russian oil sales, to reduce Putin’s revenue without throwing global energy markets into chaos.

Fourth, Washington must prevent a long war from becoming a source of weakness and distraction. The record to date is encouraging: Since February 2022, the U.S. has dialed up production of artillery shells and other weapons, while expanding and strengthening its global alliance network.

But a protracted war means an ongoing drain on U.S. resources. So it creates an imperative, as well as an opportunity, for greater outlays in the U.S. defense industrial base — in everything from securing rare-earths supply chains to stocking up on the missiles and munitions Washington would need in a conflict of its own, potentially over Taiwan.

This is all easy to say but hard to do, because the politics of the war are getting nastier although the U.S. congressional support for Ukraine remains strong. But because House Speaker Kevin McCarthy is hostage to the most obstreperous members of his Republican coalition, he is struggling to keep the U.S. government open, let alone secure another big tranche of funding for Ukraine.

Meanwhile, the three candidates who account for perhaps three-quarters of the prospective Republican primary vote — Trump, Florida Gov. Ron DeSantis and biotech entrepreneur Vivek Ramaswamy — are all skeptical, to some degree, of aid for Ukraine. Because elite sentiment usually drives popular sentiment on foreign policy, their opposition could shift views among Republican voters over time.

Don’t lose sight of what Ukraine, with Western support, has achieved: When Russian troops invaded, few thought the country would last this long or fight this well. But in a conflict that shows few signs of ending, Ukraine’s — and America’s — challenges are only beginning.

Hal Brands is a Bloomberg Opinion columnist. The Henry Kissinger Distinguished Professor at Johns Hopkins University’s School of Advanced International Studies and a senior fellow at the American Enterprise Institute, he is co-author of “Danger Zone: The Coming Conflict with China” and a member of the State Department’s Foreign Affairs Policy Board. He is a senior adviser to Macro Advisory Partners. This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.