Early in the war, many in Ukraine and the West were buoyed by the clear failure of the Kremlin’s army to conquer Kyiv and force the government to surrender, as evidenced by Russia’s shocking loss of thousands of tanks and other armored vehicles—and tens of thousands of its troops—especially on the Kyiv and Kharkiv fronts. The Ukrainian Armed Forces, in contrast, fought heroically and effectively, performing well above expectations. In response, the United States and dozens of other Western countries accelerated the delivery of weapons and ammunition to Kyiv.

As much as Ukraine welcomes every piece of equipment, however, the deliveries have been a clunky mixture of modern and antiquated, Western and Soviet. Numerous systems require specialized training, specific maintenance systems, and ammunition of various calibers that are often mutually exclusive to each weapon system. All of this requires a massive and complicated logistics system to keep the weapons supplied and functioning—one that doesn’t currently exist in Ukraine and continues to be improvised.

Meanwhile, Ukrainian leaders have been clamoring for more weapons, warning that the quantities sent or pledged so far are grossly insufficient. Ukrainian Presidential Advisor Mykhailo Podolyak wrote last week that in addition to the equipment already promised, Ukraine still needs “1000 howitzers caliber 155 mm; 300 MLRS [multiple launch rocket launchers]; 500 tanks; 2000 armored vehicles; [and] 1000 drones.” The scale of these requests illustrates how difficult it will be for the Ukrainian forces to hold out against the Russian onslaught in their country’s east, let alone turn the tide to defeat it.

Since Russia changed tack and prioritized firepower over maneuver in the Donbas fight, its forces have been pummeling Ukrainian troops with upwards of a staggering 70,000 shells per day and a significant number of heavy rockets. Additionally, Russian President Vladimir Putin’s forces are conducting as many as 300 air sorties over Ukraine per day. Ukraine, in contrast, is firing an estimated one-tenth as many shells—and sometimes flies only three to five air sorties per day.

This disparity in firepower is driving Ukrainian casualties beyond what we believe it can sustain, with up to 200 soldiers reportedly killed each day and around 500 wounded. The toll on Kyiv’s equipment is just as devastating: Most of the Soviet-era equipment Ukraine possessed at the beginning of the war has been destroyed, and it has run out of entire categories of ammunition. No military can sustain those kinds of losses and continue to offer effective resistance—as evidenced by Ukraine’s recent loss of several towns and villages to the Russian invaders and near-encirclement on the Donbas front.

Policies in Kyiv and Washington seem to ignore these battlefield realities. Last week, Zelensky reiterated his plans to regain all Ukrainian territory lost to Russia since the first invasion in 2014—currently about 20 percent of Ukraine. On the prospects for a negotiated settlement, he added one day later that “there is no time for talking” to Russia.

U.S. Deputy Defense Secretary Kathleen Hicks recently said the Pentagon is “well equipped” to support Ukraine for five, 10, or 20 years into the future. Yet our own substantial experience deployed in combat leads us to wonder if Ukraine can hold out for five to 10 months, much less one or two decades.

While there is still time, and Kyiv still controls 80 percent of its territory, a change in U.S. policy would provide a chance to save Ukrainian lives and prevent further territorial losses. At minimum, the Biden administration should de-emphasize its goals of weakening Russia and instead prioritize diplomacy, helping Kyiv and Moscow find a negotiated end to the war. It is in the U.S. national interest to prevent the war from escalating in Ukraine or expanding beyond it. Avoiding the risk of direct U.S.-Russian or NATO-Russian confrontation is vital because of the dire global consequences of a nuclear war. The world is already at a greater risk of nuclear war than at any time since the 1962 Cuban missile crisis.

By Tulsi Gabbard, a former member of the U.S. House of Representatives, and Daniel L. Davis, a senior fellow at Defense Priorities.