Georgia's top election official Brad Raffensperger has called President Donald Trump's false claims that he won the state in 2020 "just plain wrong".
Mr Raffensperger's comment came after Mr Trump pressured him in a phone call to "find" votes proving his win.
Criticism of Mr Trump's call has been widespread, with some claiming that it amounts to illegal vote tampering.
Republicans fear that the call could undermine their efforts to win two Senate races in Georgia on Tuesday.
If Republicans win one of the Georgia Senate seats in the run-off, they will retain control of the upper chamber. If both candidates lose, Democrats will control the Senate, House of Representatives and White House.
"He did most of the talking. We did most of the listening," Mr Raffensperger told ABC News on Monday.
"But I did want to make my points that the data that he has is just plain wrong."
He was on the phone for an hour to the president and his team on Saturday, and the audio was published by the Washington Post the following day. On Monday, Mr Raffensperger told reporters that he did not know the call was being recorded, and said he spoke to the president from his home.
"He [Mr Trump] had hundreds and hundreds of people he said that were dead that voted. We found two, that's an example of just - he has bad data," he added.
Gabriel Sterling, the state's voting systems implementation manager, said in a Monday news conference that Mr Trump's claims were "easily, provably false". He also rued the "ridiculousness" of the call to Mr Raffensperger.
Mr Sterling warned that the president was undermining Georgians' trust in the election process, and pleaded with residents to vote in Tuesday's election.
"Everybody's vote is going to count," he said.
What happened on the call?
Mr Trump can be heard alternately cajoling and pressuring Georgia's secretary of state to "recalculate" the vote tally.
"I just want to find 11,780 votes," he said. The number would have given him a total of 2,473,634 votes in the state, one more than Democratic President-elect Joe Biden, who received 2,473,633 votes.
He also accused Mr Raffensperger - a fellow Republican - of shredding ballots and engaging in criminal acts that cost Mr Trump the election. He called the disproven allegations "a criminal offence," adding that it presents "a big risk to you".
Mr Raffensperger responded by pointing out that Mr Trump's campaign has lost several legal challenges in court.
"The challenge you have, Mr President, is that the data you have is wrong."
What's the reaction?
On Monday, two Democratic lawmakers wrote to the FBI, asking "to open an immediate criminal investigation into the president".
"As members of Congress and former prosecutors, we believe Donald Trump engaged in solicitation of, or conspiracy to commit, a number of election crimes," wrote Ted Lieu of California and Kathleen Rice of New York.
Vice-president-elect Kamala Harris, who was in Georgia on Sunday to campaign for the Democratic senate candidates, called Mr Trump's call "a bold abuse of power".
Senate Minority Whip Dick Durbin, a Democrat, said Mr Trump was "unhinged and dangerous" and that his call to Mr Raffensperger merited "nothing less than a criminal investigation".
Georgia's Republican Lt Governor added to the criticism on Monday, telling CNN: "I am 100% certified to tell you that it was inappropriate. And it certainly did not help the situation."
"It was based on misinformation," continued Geoff Duncan, whose boss Governor Brian Kemp has faced calls from Mr Trump to resign. "It was based on, you know, all types of theories that have been debunked and disproved over the course of the last 10 weeks."
Will it affect Tuesday's election?
The Senate run-offs in Georgia have drawn national attention.
On Monday, Mr Trump, Mr Biden and Vice-president Mike Pence are all holding rallies in the state on behalf of their chosen candidates ahead of Tuesday's vote.
Speaking in Atlanta, Mr Biden urged Georgians to turn on Tuesday, saying the election's outcome could "chart the course, not just for the four years, but for the next generation".
"Tomorrow can be a new day for Atlanta, for Georgia and for America," he said.
President Trump rallied voters in Dalton, Georgia, warning that the Georgia runoff was the "last line of defence" against Democratic control of the Senate.
He said: "If the liberal Democrats take the Senate and the White House - and they're not taking this White House - we're going to fight like hell, I'll tell you right now."
He added: "This could be the most important vote you will ever cast for the rest of your life, it really could be."
The competing rallies come as nearly 3 million Georgia voters - around half of those that voted in the November general election - have already cast their ballots.
Georgia's incumbent Republican Senator David Perdue, who is fighting to hold his seat in Tuesday's race, has sided with the president.
"To have a statewide elected official, regardless of party, tape without disclosing a conversation - private conversation - with the president of the United States, and then leaking it to the press is disgusting," he told Fox News.
He also dismissed claims of wrongdoing by Mr Trump, saying: "I didn't hear anything in that tape that the president hasn't already said for weeks now since the November election."
Democratic Senate candidate Jon Ossoff said the call was "a direct attack on our democracy," and accused Mr Perdue and fellow Republican Senate candidate Kelly Loeffler of failing to defend "Georgia voters from that kind of assault".
Raphael Warnock, the other Democratic Senate candidate, called upon Senator Loeffler to "speak out against these unsubstantiated claims of fraud, defend Georgia's elections, and to put Georgia ahead of herself".
During a campaign appearance on Monday, Mrs Loeffler refused to respond to a question about the phone call, instead telling reporters: "My sole focus is on tomorrow's election."
"I am focused on that exclusively because this affects every single Georgian," she added.