The public message out of Thursday’s meeting of NATO leaders in Brussels is sure to be heavy on unity and resolve in support of Ukraine. But the unfortunate reality is that the democratic alliance confronting Vladimir Putin still isn’t doing enough to ensure the Russian’s defeat. And behind the scenes, some leaders would prefer if Volodymyr Zelensky agreed to a peace settlement sooner rather than later.

The stunning fact of this war is that the Ukrainians have rescued Europe and the U.S. as much as NATO is assisting Ukraine. Kyiv’s stalwart resistance, at great human cost, has given the West a chance to stop the advance of Russian imperialism before it imperils NATO. The war has exposed the Russian military as weaker than our intelligence services and the Pentagon thought. Against all expectations, Ukraine may be winning.

Most surprising, the Ukrainian resistance has renewed a sense among the people of the West that their countries stand for something more than welfare-state ease and individual indulgence. Ukrainians are showing that freedom has a price, often a fearsome one.

***

Yet Western leaders still seem worried of what would happen if Ukraine won. That’s especially true in the Biden Administration, which has taken many good steps—but typically under pressure from Congress or Europe, and typically late. President Biden is rightly outraged by Mr. Putin’s brutality, and he calls him a war criminal, but he still seems afraid of doing what it takes to defeat him.

At the White House on Tuesday, national security adviser Jake Sullivan was asked twice if he and the President thought Ukraine could win. The best he could offer was the assurance that Russia is “never going to be able to subjugate the Ukrainian people” and a boilerplate commitment to Kyiv’s sovereignty.

This cautious commitment extends to the slow pace of weapons delivery. Slovakia has offered its S-300 missile-defense system, which Ukraine says it needs, but it isn’t clear when it will be delivered. News leaked on March 16 that the U.S. would finally deliver Switchblade loitering drones to counter an invasion that began on Feb. 24. But on Monday the Pentagon conceded the Switchblades still weren’t on the ground in Ukraine. The U.S. should be emptying and restocking its weapons stockpiles on an emergency basis.

The same goes for assisting Western Europe as it copes with 3.5 million refugees and tries to wean itself from Russian oil and gas. The U.S. can accept many more Ukrainians for temporary protected status.

Europeans now understand the mistake they made on energy and are changing their policies. But Mr. Biden refuses to set aside his climate-change obsessions to address this world-changing crisis. His regulators are still targeting U.S. oil and gas production for slow extinction. He will have little credibility in persuading Germans and Italians to make sacrifices if he won’t help them meet their energy needs now and next winter.

It’s hard to resist the conclusion that Mr. Putin has succeeded in intimidating Mr. Biden and other leaders with his threats of nuclear escalation. This concern may justify the decision not to assist Ukraine with a NATO no-fly zone, which could require U.S. planes to attack Russian radars and missile defenses inside Russian territory.

But it shouldn’t be an excuse for caution in doing everything short of that to help Ukrainians defeat Mr. Putin. If the nuclear threat works to stop NATO support now, the Russian will use it in the future against NATO proper. The essence of deterrence is credibility, which means persuading Mr. Putin that his resort to nuclear weapons in Ukraine will be met with a requisite response. The same goes for chemical or biological weapons.

***

Our fear is that Mr. Biden, and perhaps other NATO leaders, will lean on Mr. Zelensky to agree to let Ukraine become one more “frozen conflict” like Georgia. Russia would be able to keep the Ukrainian territory it occupies in return for no more bombing. Mr. Putin would be able to consolidate control over those areas and rearm to threaten Ukraine again in the future. The NATO leaders could put that fear to rest if they said publicly that sanctions against Russia won’t be lifted until its troops leave Ukraine.

We’ve said before that a country goes to war, hot or cold, with the President it has. We want Mr. Biden to lead and succeed in Ukraine. But he needs to lead more decisively—and with a goal not merely of military stalemate but of Ukrainian victory.