Rep. Don Bacon, Sen. Angus King and H.R. McMaster, who served as Mr. Trump's national security adviser during his first administration, weigh in on the U.S.-Ukraine relationship.

Republican congressman Mike Lawler has called the tense Oval Office meeting between President Trump, Ukrainian leader Volodymyr Zelenskyy and Vice President Vance on Friday a "missed opportunity for both the United States and Ukraine," voicing guarded criticism of the American side's conduct in the diplomatic talks.