Even before taking office, Donald Trump has launched a diplomatic effort to end Russia’s war against Ukraine, calling for an “immediate ceasefire” after meeting Ukrainian President Volodymyr Zelenskyy in Paris in early December.

Trump is right to seek an end to the war. Despite a recent surge in U.S. military assistance and a greenlight for the Ukrainians to strike targets deep inside Russia, Ukraine continues to lose ground in the east, while suffering withering air attacks across its territory. Even if Russia cannot defeat Ukraine’s forces, a war that drags on indefinitely could eventually turn Ukraine into a failed state.

Still, as Trump tries to push Ukraine and Russia toward a ceasefire, he should recognize that it is in his own political interest (as well as America’s national interest) to continue providing significant support to the Ukrainians and only to accept a deal that produces a sovereign, secure Ukraine. He should stop talking about ending assistance and start making the case to a reluctant but generally obedient Republican Party that continued aid is essential to getting a durable ceasefire and ultimately defeating the Kremlin’s effort to subjugate Ukraine. Any other outcome would pose a significant threat to U.S. interests worldwide and to Trump’s standing as a world leader.