President Joe Biden pleaded with Republicans on Wednesday for a fresh infusion of military aid for Ukraine, warning that a victory for Russia over Ukraine would leave Moscow in position to attack NATO allies and could draw U.S. troops into a war.

Biden spoke as the United States planned to announce $175 million in additional Ukraine aid from its dwindling supply of money for Kyiv. He signaled a willingness to make significant changes to U.S. migration policy along the border with Mexico to try to draw Republican support.

“If Putin takes Ukraine, he won’t stop there,” Biden said. Putin will attack a NATO ally, he predicted, and then “we’ll have something that we don’t seek and that we don’t have today: American troops fighting Russian troops,” Biden said.

“We can’t let Putin win,” he said, prompting an angry reaction from Moscow.