Ukrainian servicemen load weapons last week while stationed near the village of Luhanske. (Volodymyr Petrov/European Pressphoto Agency)

Charles A. Kupchan, a professor of international affairs at Georgetown University and a senior fellow at the Council on Foreign Relations, served on the National Security Council from 2014 to 2017.

The Trump administration is in the midst of making a decision on whether to transfer lethal weaponry to Ukraine. This potential move is intended to give Ukraine’s military the ability to impose new costs on the Russians and their proxies engaged in a separatist revolt in the country’s eastern region of Donbass, thereby persuading the Kremlin to give up the fight.

But the result would likely be the opposite — an escalation in the conflict that would lead to further losses of Ukraine’s territory and compromise its political stability. Russia enjoys insurmountable military superiority over Ukraine. The United States should not encourage Ukraine to engage in an escalatory confrontation with Russia. Washington knows full well that Ukraine cannot prevail.

The urge to give Ukraine lethal arms — most likely in the form of anti-tank weapons — is understandable. Since 2014, the Russians have occupied and illegally annexed Crimea and sustained a separatist rebellion in Donbass that has claimed more than 10,000 lives. Moreover, Russia has engaged in these acts of aggression in order to block Ukraine’s desire to leave Moscow’s sphere of influence and join the community of Western democracies.

Under these circumstances, the United States should continue helping Ukrainians defend themselves by assisting with defense reforms and training Ukrainian forces. So why not take the next step and give Ukraine lethal weapons?

For starters, the notion that Russian President Vladimir Putin would give up his hold on Donbass if a few more Russians come home in body bags is to dramatically misread the Kremlin. Putin is a master at manipulating the Russian public, especially when it comes to the Ukraine conflict and would hardly fold his hand if Russian casualties were to increase.

On the contrary, he would likely double down, blaming the United States and Ukraine for the intensified fighting and taking steps to offset the improvement in Ukraine’s military capability. The Russians have so far effectively countered Ukrainian military successes — in some instances, retaliating with devastating effect. When Ukrainian forces in the summer of 2014 advanced into Donbass and took the strategically located city of Ilovaisk, Putin promptly called in his own crack troops, which quickly decimated the Ukrainian unit that had taken the town.

Should Putin decide to escalate in response to a U.S. decision to transfer lethal weapons to Ukraine, Washington would have few arrows in its quiver. Even if the Trump administration were to take another step up the ladder of escalation, Russia would go at least one step further. Russia shares a 1500-mile land/sea border with Ukraine, making the Kremlin far more invested in the fate of Ukraine than Washington. Russia has greater interest in putting skin in the game.

Rather than playing to Russia’s principal strength — its military advantage over Ukraine – the United States should continue to play to Russia’s main vulnerability — its economic weakness. On this front, the United States and its European allies, not the Kremlin, hold the cards.  The loss of income due to the low price of fossil fuels and the international sanctions imposed in response to its aggression in Ukraine have taken a serious toll on the Russian economy.  Keeping sanctions in place and, if necessary, increasing them, is the West’s best source of leverage for pushing Russia to a diplomatic solution. Congress seems to realize as much, having just imposed on the White House legislation tightening U.S. sanctions against Russia.

Sending lethal weapons to Ukraine has one further downside — it would cause a rift between the United States and its main European allies. Germany and France have been leading diplomatic efforts to find a diplomatic solution for Donbass — and both have long opposed sending lethal weapons to Ukraine because of its potential to escalate the conflict.

The United States and Europe have moved in lock step since the beginning of the conflict, closely coordinating non-lethal military assistance to Ukraine as well as economic sanctions against Russia. Transatlantic solidarity has arguably been the West’s strongest suit, confronting Putin with a united front and keeping Russia in the penalty box despite pressure from parties on both sides of the Atlantic to drop sanctions and reap the accompanying commercial benefits.

Europeans are already on edge due to Congress’s recent sanctions legislation, which imposes measures not coordinated with the European Union and that have the potential to cause undue harm to European companies. If Washington decides to head off on its own and send lethal weapons to Ukraine, solidarity on Ukraine may well come to end.

Putin has been working hard to achieve just this end. Washington would be making a serious strategic mistake if it hands to the Kremlin the transatlantic bust-up for which Moscow has long been hoping.

The conflict in Ukraine promises to poison Russia’s relations with the West until a diplomatic resolution is reached. But sending lethal weapons to Ukraine is a recipe for military escalation and transatlantic discord. The best way to bring peace to Ukraine is through transatlantic unity aimed at maintaining Russia’s political and economic isolation until it makes a deal at the negotiating table.