The impeachment inquiry into U.S. President Donald Trump’s dealings with Ukraine reached a dramatic new phase Wednesday with two senior officials testifying in the first public hearings on the controversy.

William Taylor, the top U.S. diplomat in Ukraine, and George Kent, a senior State Department official responsible for Ukraine policy, gave evidence before the House Intelligence Committee over whether Trump used military aid as leverage to secure political favors.

Read more: Trump inquiry hears new evidence of Ukraine dealings