President Vladimir Putin believes Russia's economy and its military are strong enough to weather any additional Western measures, sources said.

If Trump now permits a substantial amount of U.S. weapons to continue to flow to Ukraine, that would mark an important change. Since Trump took office, many in Ukraine and European capitals have thought that might well be the best-case scenario for Ukraine, given the U.S. president's clear hostility to continuing U.S. donations.

Russian President Vladimir Putin has sacrificed an estimated 1 million of his soldiers, killed and wounded, in a three-year campaign to crush Ukraine.