Trump is doing the worst ever seen from an incumbent going for reelection. I don't see how it could get much worse realistically.
If you mean by electoral performance, then this is certainly not the case. Herbert Hoover in 1932 and Jimmy Carter in 1980 both had as poor a standing in the polls as Trump has had, and both ended up losing by much more than he will (Hoover in the popular vote and Electoral College; Carter in the Electoral College). But if you mean from the perspective of how Trump has conducted himself in office,
especially this year, then I would agree.