Vice President Kamala Harris has razor-thin leads over former President Donald Trump in Michigan, Wisconsin and Pennsylvania, according to a new survey of the so-called “blue wall” states that could win Harris the election if she ekes out victories there.

A Sept. 11 survey by Marquette University gives Harris a four-point lead over Trump among Wisconsin’s registered voters, with a 52% to 48% matchup. This is a marked improvement for Harris since a similar survey in July, when she received 49% support among registered voters, and Trump slightly ahead with 50%.