Former Vice President Joe Biden continued to lead the field of Democratic presidential contenders in the latest poll of Wisconsin voters by Marquette University Law School.

But the poll found Biden and the other leading Democratic candidates would face a very tight race with President Donald Trump if the election were held today.

Marquette's latest poll, which was their first of 2020, was conducted from Jan. 8-12. It interviewed 800 Wisconsin registered voters and had a margin of error of plus or minus 4.1 percentage points.

Questions about the Democratic presidential primary were asked to 358 people who said they would vote in the presidential primary, giving them a wider margin of error of 6.3 percentage points.

Among those likely Democratic voters, 23 percent said Biden was their first choice, followed by Vermont U.S. Sen. Bernie Sanders at 19 percent, former South Bend Mayor Pete Buttigieg at 15 percent and Massachusetts U.S. Sen. Elizabeth Warren at 14 percent. Biden, Sanders and Buttigieg had the exact same numbers in Marquette's December survey, while Warren's support dropped by two percentage points.

Rounding out Marquette's January survey were former New York City Mayor Michael Bloomberg and entrepreneur Andrew Yang, who were each the top choices of 6 percent of voters.

Nine percent of Democrats surveyed said they didn't know who they would support. Wisconsin's presidential primary is April 7.

Marquette asked all 800 voters who they would support in hypothetical head-to-head matchups with Trump. It found Biden leading Trump 49-45 and Sanders leading 47-46. Meanwhile, Warren trailed Trump 45-48 and Buttigieg trailed 44-46. In December, Biden led Trump by 1 point and was the only candidate leading in a hypothetical head-to-head matchup.

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Trump's numbers, on the whole, were similar to his long-term trends in Wisconsin with a job approval of 44 percent compared to 52 percent who disapprove.

Asked about impeachment, 47 percent said they approved of the U.S. House of Representatives' vote to impeach Trump while 49 percent disapproved. Asked about the upcoming U.S. Senate trial, 44 percent said the Senate should convict Trump and remove him from office while 49 percent said the Senate should acquit him of the charges.

Trump's numbers barely moved despite what many international observers saw as a seismic event on the global stage — the decision by Trump to kill Iranian Maj. Gen. Qassem Soleimani with a drone strike.

Even after the decision, Wisconsin voters' views of Trump remained largely the same, with 44 percent approving and 53 percent disapproving of Trump's handling of foreign policy. In December, those numbers were 43-54.

"I think the big story is not much is changing," said Marquette University pollster Charles Franklin.

Franklin said people's views of the Democratic presidential field would likely change after the Iowa caucus and New Hampshire primary, which are both in early February.

"That's why we can all look forward to Iowa and New Hampshire shaking up the race so that we have something new to look at next time," Franklin said.