“It’s long past time for the United States to provide Ukraine the lethal defensive assistance it needs to deter and defend against further Russian aggression,” said Senator John McCain (R-Ariz.) in August—and not for the first time. McCain is arguably the most influential person in Congress on national security matters, so his words carry weight. But his is hardly a lone voice. Others, including John Herbst, who was U.S. ambassador to Ukraine from mid-2003 to mid-2006, and Alexander Vershbow, an experienced American diplomat and deputy general secretary of NATO from early 2012 until October 2016, agree with McCain. So do former President Bill Clinton’s deputy secretary of state, Strobe Talbott, and a cluster of diplomatic and national security luminaries, who came out of the gate early on this issue in a report released in 2015.

The efforts of these individuals haven’t been in vain. U.S. President Donald Trump will soon decide whether to implement their proposal, and key members of his national security and military team favor doing so, according to recent statements from General Joseph Dunford, chairman of the Joint Chiefs of Staff, and Kurt Volker, Trump’s top negotiator on the Ukraine crisis. Defense Secretary James Mattis has confirmed that the option was being “actively reviewed.”

Arming Ukraine won’t make Putin cry uncle.

Those who call for sending lethal arms to Ukraine (the United States and some of its NATO allies already train Ukrainian troops, and the United States has been providing nonlethal arms to Ukraine to the tune of $300 million in 2016 alone) claim that American weaponry will strengthen Kiev’s hand and compel Russian President Vladimir Putin to negotiate a just political settlement that ends the war in Ukraine’s Donbas region.

They’re misguided. Worse, their proposal could be dangerous, for Ukraine and the United States.

Arming Ukraine won’t make Putin cry uncle. Past experience—notably Moscow’s stepped-up intervention to save its Donbas clients in the battles for Ilovaisk and Novoazovsk in 2014 and 2015 and Debaltseve in 2015—suggests that Putin will continue to reinforce Russia’s proxies, especially if they suffer setbacks at the hands of better-armed Ukrainian troops.

A pro-Russian separatist near Donetsk, August 2014. Maxim Shemetov / reuters

Because Russia and Ukraine share a border, Putin can send forces and weapons to the battlefield far faster than the United States can resupply Ukraine. Most importantly, Ukraine matters far more to Russia than to the United States. Indeed, even the advocates for arming Ukraine disavow any intention to send American troops to fight for the Ukrainians, knowing full well that such a recommendation would doom their efforts.

By contrast, Putin hasn’t hesitated to order Russian troops into battle in the Donbas, where many have been killed. His popularity ratings nevertheless remain sky-high. Eighty-seven percent of Russians support his handling of foreign affairs—about the same as did in 2014. There is no evidence that the war in Ukraine has dented Putin’s popularity, let alone enabled opposition leaders to mobilize support against his government. Yet proponents of providing Ukraine lethal arms suggest that because of the bite of Western sanctions and Russians’ mounting unhappiness with the war, Putin desperately wants to escape what they portray as the Donbas quagmire.

In fact, although Russia has now endured political isolation and Western economic penalties for over three years as a consequence of Putin’s annexation of Crimea and instigation of the war in eastern Ukraine, he has not made a single significant concession or shown any inclination to sacrifice the Donbas insurgents. Instead, he has stuck by them and, as his military escalations in 2014 and 2015 show, bailed them out when necessary.

The proposition that Putin won’t be provoked by a U.S. decision to send lethal arms to Ukraine amounts to a hunch. It’s not supported by evidence, and Putin’s past behavior contradicts it. This is not a minor point: if he does ramp up the war and the Ukrainian army is forced into retreat, the United States will face three bad choices.

The proposition that Putin won’t be provoked by a U.S. decision to send lethal arms to Ukraine amounts to a hunch.

First, Washington could pour even more arms into Ukraine in hopes of concentrating Putin’s mind; but he can easily provide additional firepower to the Donbas insurgents. Second, it could deepen its military involvement by sending American military advisers, or even troops, to the frontline to bolster the Ukrainian army; but then Russia could call America’s bluff. Third, the United States could decide not to respond to Russia’s escalation given the geographical disadvantage and the limited strategic interests at stake. That would amount to backing down, abandoning Ukraine, and shredding the oft-repeated argument that American and European security hinges on the outcome of the Donbas war.

Proponents of arming Ukraine say that things will never reach this point because their goal is merely to force a political settlement that’s acceptable to Ukrainians and ends a war that has killed some 10,000 people. The point, they insist, isn’t to empower Kiev to crush the Donbas rebels, and they dismiss the possibility that an American-armed Ukraine might be emboldened to attempt just that.

Yet in a speech at West Point in September, Ukrainian President Petro Poroshenko declared that his intent was precisely to retake the Donbas (a point that he also made earlier in July and again in October), and he noted that American weapons would help him succeed. Surely, Poroshenko’s words matter more than breezy assurances from those pushing to arm Ukraine.

The supporters of arming Ukraine also shortchange that country's military capabilities. The Ukrainian army has nearly doubled in size, from 130,000 in 2014 to 250,000 today, and is now one of Europe’s largest. In 2018, Ukraine’s military spending will increase by a quarter to $6.3 billion (or five percent of GDP), more than double the 2014 figure.

In addition to the increases in defense spending and the size of its army, Kiev has taken other steps to beef up its security. The draft was reinstituted in 2014. Ukraine has been improving its command, control, surveillance, and intelligence network and acquiring more, and better trained, special operations forces. With help from NATO’s Comprehensive Assistance Package, which was adopted in 2016, it is revamping the administration of its armed forces.

Ukrainian President Petro Poroshenko at a ceremony commemorating the 70th anniversary of the end of World War II in Kiev, May 2017. Valentyn Ogirenko / REUTERS

True, there are many obstacles to transforming Ukraine’s military, corruption among them. The goal of bringing it up to NATO standards by 2020 may amount to wishful thinking. And progress will be slow under the best of circumstances. Yet the Ukrainian army of today is certainly not what it was in 2014—a shell.

What’s more, Ukraine is no slouch in building weapons. Ukroboronprom, the state weapons manufacturer, employs 80,000 people and oversees 21 affiliates, and there are some 36 private Ukrainian defense firms besides. Ukraine makes advanced tanks, armored amphibious vehicles, aerial refueling tankers, transport aircraft, laser-guided anti-tank missiles (which get top billing in proposals to arm Ukraine, never mind that Ukraine makes the Corsar and Stugna-P laser-guided ATGMs), and long-range early-warning radars. Moreover, Ukraine was the world’s ninth-largest arms exporter from 2012 to 2016. It earned over $500 million selling arms last year and a total of $11 billion since it became an independent country. In short, the clamor to arm Ukraine may have less to do with its dire need for weapons than with drawing the United States deeper into the conflict.

Supporters of arming Ukraine insist that this move is also essential for reassuring NATO and preserving Europe’s peace. Yet the proposition that the United States should risk getting enmeshed in a war on Russia’s doorstep to soothe its skittish NATO states makes no sense. Article V of the pact’s treaty already provides that a member that comes under attack will be defended, with military force if needed. Moreover, although Trump declared NATO “obsolete,” he later reversed himself, and there is every reason to believe that his administration remains committed to the transatlantic alliance.

If NATO truly seeks to become stronger and Europe is indeed so vulnerable and edgy, the alliance’s wealthy European members should take some big steps at home, such as boosting defense spending. Although some have, many have not. The alliance’s figures show that only five of its 27 European states now spend two percent or more of their GDP on defense, the target accepted in 2006. NATO’s European members also have much work to do on other fronts. These include reducing duplication in the production of major armaments and increasing inter-operability and the capabilities for the rapid deployment of forces to the battlefield. Substantial progress in these areas, not reassurances about Washington’s dependability as demonstrated by the dispatch of American arms to Ukraine, are what the alliance needs.

The case for arming Ukraine also tends to be made in a vacuum, never mind that what the United States does in Ukraine could determine what Russia does elsewhere. Moscow could respond by putting more pressure on the Baltics, acting as a spoiler in North Korea or Iran, or even arming the Taliban (that would be an ironic turn: in the 1980s, the United States bled the Soviets by arming the Afghan mujahideen). If these outcomes seem impossible, consider the United States’ awful record in foreseeing the effects of its military moves. In Vietnam, Kosovo, Afghanistan, Iraq, and Libya, adversaries didn’t respond the way Washington anticipated, or there were dangerous unintended consequences. Russia, for its part, surprised the United States by sending its troops into Georgia in 2008, Crimea in 2014, and Syria in 2015.

All in all, the plan to pressure Putin by providing Ukraine lethal arms is strategically flawed. Worse, it could prove reckless.