The judicial process is about President Donald Trump abusing his power and hindering the work of Congress - the two formal state prosecutions recently approved in the House of Representatives.
Several senators were seen several hours before its stretch, looking at the clock again and whispering to each other, before Republican Majority Leader Mitch McConnell announced a half-hour dinner break.
"Most senators ran for the door, boring students during the last school day," CNN writes.
Voted down
The agenda includes discussing the procedure and the rules for the rest of the trial.
Republicans also stopped several Democrats' attempts to solicit evidence and call witnesses. The members voted according to the party line with the votes 53-47.
As the debate dragged on over time, McConnell offered the Democrats to merge all their demands into a joint vote, to speed up the process, which the minority leader, Democrat Chuck Schumer, rejected.
- There will be a number of votes. We are willing to do some of them tomorrow. There is no need to do everyone tonight if it is awkward for the Senate and Chief Judge. But we will not back down to getting votes on all of these additions, Schumer said according to Fox News.
Did Trump pressure Ukraine?
The big question during the trial is whether Trump can be considered to have pushed the Ukrainian government to interfere in the upcoming US presidential election this fall.
Democrats accuse the president of conditional on the payment of a major military support package demanding that Kiev announce an investigation into Trump's potential rival, Democratic presidential candidate Joe Biden.