"I think the Senate is tough actually. The Senate is very tough," Mr Trump said, according to an anonymous attendee.
“There are a couple senators I can't really get involved in. I just can't do it. You lose your soul if you do. I can't help some of them. I don't want to help some of them.”
Hours after the Post published the article, Mr Trump told reporters in Wisconsin before a campaign rally there that he “hoped” the Senate would remain in Republican hands.
"I hope to hold the Senate, we do. I think from a presidential standpoint we're winning a lot of states including this one,” said Mr Trump.
“I think we're doing very well here. The crowd is certainly enthusiastic. I hope that we do. I think we're gonna take back the House because people are tired of Nancy Pelosi. I think we'll take back the House.”
The Republicans currently control the Senate with a 53-47 majority, but pollsters say that Democrats have a chance to take it back on election day.
Mr Trump has even gone after at-risk Republican Senators, including Maine’s Susan Collins, after she opposed his Supreme Court nomination of Amy Coney Barrett.