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 Trump’s “trifecta” of offenses.

The day started with a setback for Republican Senate leader Mitch McConnell and the president’s 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, Trump’s 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.