U.S. President Donald Trump says he wants to bring peace to Ukraine. But his approach cannot work, because it fails to address the problem of security guarantees. There will be no peace as long as Ukraine must face Russia on its own. But perhaps this flaw can be overcome. In theory, technical innovation in the miniaturization of warfare might offer new ways of ensuring peace, and France and the United Kingdom — both nuclear powers — could step in as America steps back. Now is the time to consid