WASHINGTON (AP) The U.S. Senate plunged into President Donald Trump s impeachment trial on Tuesday with Republicans abruptly abandoning plans to cram opening arguments into two late-night sessions and Democrats arguing for more witnesses to expose Trumps trifecta of offenses.

The day started with a setback for Republican Senate leader Mitch McConnell and the presidents legal team, exposing a crack in the GOP ranks and the growing political unease over the historic impeachment proceedings unfolding amid a watchful public in an election year. But it was ending with solid Republican rejection of Democratic demands for witnesses.

Chief Justice John Roberts gaveled open the session, with House prosecutors on one side, Trumps team on the other, in the well of the Senate, as senators sat silently at their desks, under oath to do impartial justice. No cellphones or other electronics were allowed.

Opening day stretched deep into the night. Senators remained as the clock passed midnight, while Democrats pursued what may be their only chance to force senators to vote on hearing new testimony. Tempers flared as lawerly arguments gave way to more pointedly political ones.

After one particularly bitter exchange, Roberts intervened, taking the rare step of admonishing both the Democratic House managers and the White House counsel to remember where they are.

I think it is appropriate at this point for me to admonish both the House managers and the presidents counsel in equal terms to remember that they are addressing the worlds greatest deliberative body, the usually reserved Roberts said. He asked them to avoid speaking in a manner and using language that is not conducive to civil discourse.