The poll for the first time tested Pete Buttigieg, the Midwestern mayor running in part on his regional credentials being an advantage over Trump. He trailed the president by 2 points, 45 percent to 43 percent, with a higher number of undecideds (7 percent) than any of the other potential matchups.

Biden’s strength in states like Wisconsin is central to his campaign, which argues that he’s the strongest Democrat to take on Trump in 2020 and could win back disillusioned Midwestern voters who flipped key states to Trump in 2016. Trump claimed Wisconsin by fewer than 23,000 votes, and it’s become a top target of Democratic leaders, who are holding their national convention in Milwaukee next summer.

The survey also found Biden with an early lead in Wisconsin’s April 2020 Democratic primary, at 31 percent followed by Warren at 24 percent. Sanders got 17 percent support in the primary test, while Buttigieg came in at 7 percent, Kamala Harris got 5 percent and every other candidate got 3 percent or less.

Warren was the second choice of 27 percent of respondents, followed by Biden (19 percent), Sanders (13 percent), Buttigieg (10 percent) and Harris (9 percent).

Marquette also looked at impeachment, finding that support in Wisconsin for impeachment has grown since April, to 46 percent — but that 49 percent of respondents believe there is not enough evidence to launch congressional impeachment hearings.

Among those who said they have read the rough transcript of a conversation between Trump and the Ukrainian president, which has become a key piece of evidence in the investigation, 51 percent said they think there’s enough reason to hold impeachment hearings, compared with 42 percent among those who have not read the summary of the phone call.

The survey of Wisconsin registered voters was conducted Oct. 13-17 and has a margin of error of plus or minus 4.2 percentage points.