That fact-based comment prompted a broadside from the former President, who called Rounds a "jerk" and "ineffective" and vowed "never" to endorse Rounds for reelection, though he's not facing voters again until 2026.
"Is he crazy or just stupid?" Trump said in a statement.
Rounds, who has a low-key and genial demeanor and is well-regarded by his colleagues, stood by his comments -- and said he was "disappointed but not surprised" by Trump's statement. Rounds told CNN on Tuesday that Republicans need to speak the truth to voters about 2020 so they can have trust in the results of free and fair elections in 2022 and beyond.
"Nobody is out looking for confrontations," Rounds said, defending his remarks. "What we are looking for is to be able to provide good information in a timely fashion, but to be seen as being responsible and being honest. I think that's what the American people deserve. And I think that's what many of us want to do. We're not looking to fight. What we're looking is, is to say here are the facts, and they're not going to change."
Rounds added: "Why are we having that discussion today? I think because we're getting closer and closer to 2022, in which we want people to get out and vote. We want them to have faith in the election process. We want them to feel like they're a part of it and that their vote really matters."
Even some Trump allies came to Rounds' defense on Tuesday.
"I've always said I agree that the election was not stolen -- at least to the degree that it was illegal theft," said Sen. Kevin Cramer, a North Dakota Republican who contended Democrats took advantage of more voting rules eased during the pandemic. "I've moved on a long time ago, and most members of Congress have, including Mike."
Other Republicans said it was time to focus on something other than 2020.
"I say to my colleague, welcome to the club," Sen. John Thune, the senior South Dakota Republican said of the Trump attack on Rounds -- something he has endured himself in the past. "I don't think re-litigating or rehashing the past is a winning strategy.
If we want to be a majority in 2023, we've got to get out and articulate what we're going to do with respect to the future the American people are going to live and the things they're going to care about when it comes to economic issues, national security issues."
Many Republicans were angered over the personal nature of Trump's attacks against Rounds, who lost his wife in November after a battle with cancer.
"I take great exception to anybody that calls Mike Rounds a jerk," said Sen. Shelley Moore Capito, a West Virginia Republican. "Because he's one of the kindest, nicest, most sincere members that we have."
Still, some Republicans wanted to stay above the fray.
"Nothing to add to what's already out there," Sen. John Barrasso, a Wyoming Republican, and member of GOP leadership, said when asked about the episode.