President Donald Trump fired two key impeachment witnesses on Friday.
The administration sacked Gordon Sondland, the ambassador to the European Union, shortly after it had removed Lt Col Alexander Vindman from his White House post.
Both Scondland and Vidman provided testimony in Trump’s impeachment trial.
The House of Representatives approved two articles of impeachment against Trump in December.
The charges stem from Trump’s repeated efforts to have Ukraine publicly announce criminal investigations into Democratic front-runner Joe Biden.
Conviction on either charge would have resulted in Trump’s removal from office.
Trump is the third president in U.S. history to face a Senate impeachment trial.