The U.S. Senate race in Wisconsin has tightened to its narrowest margin to date in the Marquette Law School Poll.

Former Democratic Sen. Russ Feingold leads incumbent Republican Sen. Ron Johnson 46-44 among likely voters. Libertarian candidate Phil Anderson received 4 percent support.

Johnson has trailed in every publicly available poll tracked by Real Clear Politics dating back to February 2015 with the exception of a Loras College poll conducted last week that showed him five points ahead of Feingold.

Two other national polls last week showed Feingold leading by margins of 3 points and 12 points.

Marquette poll director Charles Franklin said as the race has gotten closer to Election Day partisans on both sides have closed ranks behind their respective candidates. Only 7 percent of Republicans and 5 percent of Democrats said they would cross over and vote for the other party’s candidate.

“This looks like a perfectly understandable, highly partisan race,” Franklin said.

The previous Marquette poll showed Johnson down six points, which was a poorer showing than GOP presidential nominee Donald Trump at the time, who was trailing Democrat Hillary Clinton by three points in a four-way race. That poll was taken just before the first presidential debate.

In the latest poll, Johnson is faring better than Trump, who trails Clinton by seven points.

It’s unclear what impact, if any, Trump’s troubles are having on the U.S. Senate race, though Feingold’s campaign issued a statement linking Trump to Johnson. After downplaying the Loras College poll earlier in the day, the campaign characterized the race as “close.”

“Sen. Johnson is trying to hide his record of protecting a system that benefits corporations and multimillionaires like himself in a desperate attempt to stay in Washington and save his political career,” spokesman Michael Tyler said. “And he’s continuing to cling to Donald Trump, despite the fact that his Republican colleagues are repudiating his disgusting actions.”

Johnson’s campaign issued an internal memo touting Johnson’s $4 million fundraising haul in the third quarter and more than 2 million voter contacts. Feingold has yet to release his third-quarter fundraising figures.

“As we’ve consistently said, this is going to be a tight race with a real choice for Wisconsinites – between an Oshkosh manufacturer getting things done and a 34-year career politician saying one thing and doing another,” Johnson spokesman Brian Reisinger said.

Johnson’s name recognition and favorable rating have increased markedly since the previous Marquette poll among likely voters. Last month 39 percent viewed him unfavorably and 35 percent viewed him favorably, while 26 percent had no opinion.

This month he improved to 43 percent favorable, 37 percent unfavorable and 20 percent with no opinion.

On those same measures Feingold has dropped from 48 percent favorable, 32 percent unfavorable last month to 45-40 in the latest poll. Those without an opinion declined from 20 percent to 15 percent.

Franklin said Johnson’s improving numbers might be explained by voters paying more attention heading into the final month of the election and Republicans rallying around their candidate.

The poll included 878 likely voters and a margin of error of +/-3.9 percentage points.

Feingold and Johnson meet for the first of two debates on Friday.

Capital W: Plug in to Wisconsin politics

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Percentage of respondents who would vote for candidates in the most recent Wisconsin polls.