Democrat Russ Feingold has reopened a significant lead over Republican U.S. Sen. Ron Johnson, 50 percent to 36 percent, in the new Marquette Law School Poll released Wednesday.

That’s compared to the last Marquette poll in August, which showed Feingold with a narrower lead at 47 percent to 42 percent.

Marquette Law School Professor Charles Franklin, director of the poll, said the race — viewed nationally as one of the leading U.S. Senate contests and a key to helping Democrats regain a majority — likely will continue to fluctuate in the near term.

Just 55 percent of poll respondents were able to say if they have a favorable or unfavorable view of both Johnson and Feingold, Franklin said. Until voters become more informed, Franklin said that’s a recipe for continued volatility in polls of the race.

“Many voters have not yet tuned in,” Franklin said.

The Marquette poll was conducted by phone Sept. 24-28, with 803 registered Wisconsin voters. Both landline and cellphones were used. The margin of error for the poll is plus or minus 4.1 percentage points.

Feingold’s campaign spokesman, Tom Russell, hailed the poll results in a statement.

“This is going to be a hard-fought race, but it’s clear Russ continues to lead the incumbent senator in polling because he’s running a campaign built on listening to Wisconsinites and fighting for middle class and working families,” Russell said in a statement.

The August poll showed tightening in the Johnson-Feingold race. The Marquette poll preceding that one, which came out in April, had Feingold leading Johnson 54 percent to 38 percent.

Johnson spokesman Brian Reisinger cited that fluctuation in responding to the latest results.

“The wild swings in these early polls show just how meaningless they are,” Reisinger said. “Sen. Feingold led all the early polls in 2010 — until Wisconsinites proved the professional political class wrong.”

The partisan breakdown of respondents to this Marquette poll, including those who lean toward a party, was 49 percent Democratic, 40 percent Republican and 9 percent independent.

Feingold is from Middleton; Johnson is from Oshkosh.