Donald Trump launched a fresh attack on governor of Michigan Gretchen Whitmer just weeks after she was the victim of a right-wing militia kidnap plot.
Earlier Mr Trump lashed out at a Republican senator who warned that the president will inspire a GOP “blood bath” on Election Day.
He said that the president “regularly sells out our allies under his leadership” while he “spends like a drunken sailor."
“He mocks evangelicals behind closed doors," Senator Sasse said. "He's flirted with white supremacists."
Mr Trump hit back in a pair of tweets comparing “little” Sasse to Bob Corker and Jeff Flake, two other GOP senators who feuded with the president.
He said: “Both Senators became totally unelectable, couldn’t come even close to winning their primaries, and decided to drop out of politics and gracefully “RETIRE”. @SenSasse could be next, or perhaps the Republicans should find a new and more viable candidate?”
Meanwhile, with less than three weeks so Election Day, the president said he “won’t feel so good” if he loses to Joe Biden, as more than 25 million voters have already cast their ballots.
“Could you imagine if I lose?” he told rallygoers on 16 October. “I’m not going to feel so good. Maybe I’ll have to leave the country, I don’t know.”
The president headed to rallies in Wisconsin and Michigan on Saturday, despite both states reporting their largest single-day case counts since the onset of the public health crisis.
As the nation surpasses 8 million infections and is climbing its way into a third “surge" of cases and hospitalisations, Michigan reported its second consecutive day of more than 2,000 confirmed cases on Friday.
Wisconsin health officials reported three consecutive days with more than 3,000 cases. On Friday, the state recorded more than 4,000.
Nearly 70,000 coronavirus infections were reported in the US on Friday, marking the nation’s single highest confirmed daily case count since July.