They're not threatening to do that. They just did. Read the tweet linked in the article.

> In conjunction with the President's directive for the Federal Government to cease all use of Anthropic's technology, I am directing the Department of War to designate Anthropic a Supply-Chain Risk to National Security. Effective immediately, no contractor, supplier, or partner that does business with the United States military may conduct any commercial activity with Anthropic. Anthropic will continue to provide the Department of War its services for a period of no more than six months to allow for a seamless transition to a better and more patriotic service. https://x.com/SecWar/status/2027507717469049070?s=20

This has never happened before. It just goes to show how overextended the USG is these days. America is broke. Anthropic is about to IPO. Most stock market money comes from foreign countries like Japan these days. All those people are going to trust Anthropic more if they believe the company is neutral among nations and acting as a check and balance to power.

"This has never happened before." US could compel Anthropic to act; simply not doing business with them is restraint, not escalation.