Joe Biden leads President Donald Trump by 9 percentage points in a hypothetical general election matchup in Wisconsin, one of the key states the president snatched from Democrats to win the White House in 2016.

A Marquette University Law School poll released Wednesday shows Trump’s approval among registered Wisconsin voters at 45 percent, while 53 percent disapprove of Trump.

The poll also shows Sen. Bernie Sanders leading Trump in a head-to-head contest by a 4-point margin, while Sens. Elizabeth Warren and Kamala Harris were tied with Trump in the survey. In each case, Trump’s numbers hovered in the 40s, which the Marquette poll's director sees as an indicator of Wisconsin voters' strong, baked-in feelings about the president.

“That simply reflects how strongly voters feel about Trump, both pro and con. He has a very strong committed base that gets him into the 40s,” said Charles Franklin, director of the Marquette Law School poll. “But there are not enough swing voters, at least at this point, that can boost him out of the 40s.”

Franklin said Marquette polling shows Trump's approval rating in Wisconsin has not fluctuated significantly so far during his term in office.

The survey of 800 Wisconsin registered voters was conducted Aug. 25-29 and has a margin of error of plus or minus 3.9 percentage points.

Biden’s 9-point advantage in the poll underscores the central argument of the former vice president’s candidacy: his electability. Biden’s campaign contends that he is the best-positioned Democrat to beat Trump in 2020, maintaining that he would attract disillusioned Midwestern voters who flocked to Trump three years ago.

“It’s a pretty strong showing for Joe Biden. He’s also in first place among Democratic primary voters in a state that Bernie Sanders won over Clinton pretty significantly,” Franklin said.

Among Democrats and Democratic leaners, 28 percent said Biden was their first choice for the Democratic presidential nomination, while 20 percent picked Sanders and 17 percent picked Warren. No other candidates drew more than 6 percent.

“The caveat of course is how early it is and how much things can change," Franklin said. "I do think that’s an important point, that we are still early in the process. While several of the candidates have visited Wisconsin, we’re certainly not the focus of the primary electorate right now.”

Hillary Clinton skipped Wisconsin in the 2016 general election, as Democrats took for granted the state's history of favoring their party in presidential elections. Trump ended up claiming the state by less than 23,000 votes, and since then, no state has been more symbolic of Democrats’ quest to oust Trump. The Democratic National Convention will take place in Milwaukee next summer.

Last year, Democrat Tony Evers ousted longtime popular GOP Wisconsin Gov. Scott Walker, an event Democrats point to as a sign of organizational strength in the state. But that election was a nail-biter, even as Democrats swept midterm elections across the country in 2018.