Some, like Perkins, want to take on the Russians directly. Others, including Burgart and Turner, have sought less risky ways to get involved, offering military and first-aid training, hauling humanitarian supplies, and setting up contacts for future American volunteers to assist Ukrainians.

“This,” said Perkins, a Navy veteran who resides in San Diego, “is a noble cause.”

While President Biden has said repeatedly and emphatically that U.S. troops will not be pulled into the conflict, the government of President Volodymyr Zelensky has actively recruited Western military veterans to join its newly formed International Legion of Territorial Defense of Ukraine. An estimated 20,000 foreigners have expressed interest, the Ukrainians say. About 4,000 are Americans, said an official with the Ukrainian Embassy in Washington, who spoke on the condition of anonymity because the issue is seen as highly sensitive in Washington. It’s unclear how many may follow through…

“For me personally, this feels so unprovoked,” said Burgart, who saw combat in Iraq while serving in elite Marine Corps reconnaissance units. “It’s just insanity to me. I don’t want insane people to be able to do insane things in the world.”