The U.S. and its NATO allies must remain united as they work to sustain support to Ukraine, Army Secretary Christine Wormuth said.

“We can’t take that unity for granted, but I think our NATO allies know what’s at stake,” Wormuth said May 31 during an event hosted by the Atlantic Council.

However, the alliance must find a balance between aiding the Ukrainians and not escalating the war.

“Where the U.S. stands is wanting to provide all of the assistance we can to the Ukrainians without escalating the situation to a point where the war spills over or goes in a terrible direction,” she said.

There have been discussions about what happens if Russian President Vladimir Putin starts to feel cornered, Wormuth said. “Would he lash out? Would he contemplate chemical weapons or, more horrifically, some sort of tactical nuclear demonstration?”

The U.S. must “very prudently measure those risks and think very carefully about how can we best give the Ukrainian military what they need,” she said.

The Ukrainians are facing a “grinding artillery battle,” she said. “It’s going to be more challenging, frankly, to sustain the morale of the Ukrainian forces given the bombardment they’re being subject to, but, again, we cannot allow this war to escalate.”

The U.S. and NATO aren’t the only ones who must measure their actions. 

“I think if Putin were to decide to use some sort of tactical nuclear demonstration, that would erase, in my mind, any possibility that he could be anything other than a pariah leader, leader of a pariah state, for decades going forward,” Wormuth said. “I think that Putin would have to think extremely long and hard about that since he clearly wants to try to bring Russia back into the international community at some point. I don’t see how he does that if he goes nuclear.”