U.S. Sen. Susan Collins did not lead in a single publicly released poll during the final four months of her re-election campaign in Maine. But Collins, a Republican, won the election comfortably.

Sen. Thom Tillis, a North Carolina Republican, trailed in almost every poll conducted in his race. He won, too.

And most polls underestimated President Donald Trump’s strength, in Iowa, Florida, Michigan, Texas, Wisconsin and elsewhere. Instead of winning a landslide, as the polls suggested, Joe Biden beat Trump by less than 2 percentage points in the states that decided the election.