WASHINGTON - US Senate Minority Leader Chuck Schumer said Sunday that senior administration officials must testify in President Trump's impeachment trial after a report that Trump told a former aide to hold up military aid to Ukraine pending investigations into political rivals.In a tweet, Schumer said Republicans must back efforts to call former national security adviser John Bolton, among others, to testify.Citing descriptions of Bolton's unpublished manuscript, the New York Times reported Sunday that Trump told Bolton in August he wanted to continue withholding $391 million in aid until Ukranian officials provided information about investigations into Vice President Joe Biden, among others.