United States support for Ukraine has been weakened after years of progress in aiding the former Soviet satellite state and applying pressure on Russian President Vladimir Putin, top impeachment witness Kurt Volker said.

“It is a tragedy for the United States and for Ukraine that our efforts in this area, which were bearing fruit, have now been thrown into disarray,” Volker, who resigned as the lead U.S. negotiator for the war in Ukraine as the impeachment controversy erupted, told lawmakers Tuesday.