The Senate Democratic leader's letter comes amid President Donald Trump's ouster of key government officials in the impeachment probe.

Saturday Night Live would also be hosted for the first time by drag queen legend RuPaul, while Justin Bieber returned as a musical guest.

Lt. Col. Alexander Vindman and U.S. Ambassador to the European Union Gordon Sondland both say they've been asked to leave the administration.

"It was evil, it was corrupt,'' Trump declared at the White House. "This should never ever happen to another president, ever.''

Mitt Romney, a moderate and elder statesman in his party, is the only Republican senator to announce that he plans to vote to remove Trump from office.

The trial is cruising to impeachment tallies that will fall short of even a majority of the GOP-held Senate, much less the two-thirds required to remove Trump from office and install Vice-President Mike Pence.

Trump is virtually certain to be acquitted, and no member of either party has indicated yet that they will break with their party colleagues.

By a vote of 51-49, the Republican-controlled Senate stopped Democrats' drive to hear testimony from witnesses.

The impeachment trial of Donald Trump has become alternately confusing, irritating and underwhelming, Roy Green says.

The move could all but dash Democratic efforts to hear more testimony and boost odds the Senate will vote to acquit Trump as early as Friday.