President Trump's lawyers have begun defending him at his impeachment trial, accusing Democrats of seeking to overturn the result of the 2016 election.
"The president did absolutely nothing wrong," White House Counsel Pat Cipollone said.
Mr Trump's defence will last three days and follows the Democrats' prosecution case which ended on Friday.
The president faces two charges linked to his dealings with Ukraine.
The charges, or articles of impeachment, accuse him of abuse of power and obstruction of Congress.
He is alleged to have withheld military aid to pressure the Ukrainian President, Volodymyr Zelensky, into starting a corruption investigation into Mr Trump's political rival, Democrat Joe Biden, and his son Hunter.
Democrats also accuse Mr Trump of making a visit by Mr Zelensky to the White House contingent on an investigation.
Mr Trump is charged with obstructing Congress by failing to co-operate with the House of Representatives impeachment inquiry.
The president dismisses the accusations as a witch-hunt.
What else did the defence say?
The trial in the Senate will decide if Mr Trump should be removed from office. This is unlikely as the Republicans control the Senate and any such move would need a two-thirds majority.
Echoing a line heard from many Republicans, Mr Cipollone said Democrats were "asking you not only to overturn the results of the last election... they're asking you to remove President Trump from the ballot in the election that's occurring in approximately nine months."
"They are asking you to do something very, very consequential and, I would submit to you ... very, very dangerous," he said.
Much of the abuse of power charge centres on a phone call in July between Mr Trump and Mr Zelenksy.
Trump defence lawyer Mike Purpura insisted there was no quid pro quo - as asserted by the Democrats.
"Zelenksy felt no pressure. President Zelensky says he felt no pressure. The House managers tell you they know better," he said.
How have Democrats reacted?
In a news conference after Saturday's hearing, Adam Schiff, the Democrats' lead prosecutor, raised the disputed issue of calling witnesses.
"The one question they did not address at all is why they don't want to give the American people a fair trial, why they want this to be the first impeachment case in history without a single witness and without a single document being handed over.
"That ought to tell you everything you need to know about the strength and weaknesses of this case".
The leader of the Democrats in the Senate, Chuck Schumer, told reporters that Mr Trump's defence team had inadvertently "made a really compelling case for why the Senate should call witnesses and documents".
Deeply political trial
By Chris Buckler, BBC News, Washington
Rather than focus just on detail the president's lawyers did their best to paint the whole impeachment process as an attempt to undermine the vote that put Donald Trump into office... not anything to do with his conduct while serving in it.
A couple of miles away in the White House the commander-in-chief's primary worry seemed to be TV ratings. He's said to be upset that his attorneys were given a Saturday to start setting out their defence - a day which he says is a "death valley" for TV ratings.
In a post on Twitter he encouraged his supporters to tune in and said a number of things his lawyers couldn't in a fierce attack on his political opponents.
The Democrats are just as aware of the television cameras. At the start of the hearing they rolled in a 28,000 page record of the trial so far, complete with evidence already presented to the Senate.
The Republican party leadership has made no secret that they want this trial over as quickly as possible, so they may have been pleased to hear that Mr Trump's lawyers don't intend to use all of the 24 hours allotted to them to make their case.
However this short opening session gave only a taste of what's to come.
Many are expecting the arguments on Monday and Tuesday to be rather more pointed. If that proves to be true, it will only fuel suspicions that everyone in this deeply political trial is speaking to voters as much as the senators inside the chamber.
Where does the trial go from here?
Saturday's session was unexpectedly short - two hours. The second day of defence arguments resumes on Monday at 13:00 local time (18:00 GMT) allowing for a short weekend break.
Once the third day of defence arguments is over, senators will have the chance to submit written questions to the House prosecutors and White House lawyers through Chief Justice John Roberts, who is presiding over the trial.
Senators are also expected to debate whether to allow new witnesses to be called and fresh evidence submitted.