Ron Johnson, Russ Feingold mashup (copy) (copy)

Former Democratic Sen. Russ Feingold, right, is challenging Republican Sen. Ron Johnson for the seat he lost in 2010. archives

The Senate race between Republican Sen. Ron Johnson and Democratic former Sen. Russ Feingold is tightening, according to a new poll of Wisconsin voters.

In the last Marquette University Law School Poll, conducted about a month before Feingold announced his candidacy in May, the longtime senator held a 54-38 lead against Johnson, who ousted him in 2010.

According to Thursday's Marquette poll, conducted Aug. 13-16, Feingold's lead has gotten smaller. Among registered voters, Feingold now receives 47 percent, compared to Johnson's 42 percent.

That's a "noticeable tightening," but not a surprising one, said poll director Charles Franklin.

But despite Feingold having served 18 years in the Senate and Johnson being a current officeholder, many voters still don't know enough about the candidates to have an opinion.

Twenty-seven percent of voters have no opinion of Feingold, up slightly from 26 percent in April. For Johnson, 38 percent have no opinion, down a tick from 39 percent in April.

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"Sen. Johnson has been high in non-recognition, non-rating, compared to Sen. Baldwin over that period of time ... now, Baldwin did run more recently than Johnson," Franklin said. "Sen. Johnson does seem to be less well-known than a number of other senators, though I wouldn't say he's totally unique (in that)."

In Thursday's poll, Sen. Tammy Baldwin earned a 36 percent favorable rating, down from 39 percent in April. Twenty-four percent had no opinion, compared to 23 percent in April.

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Jessie Opoien covers state government and politics for the Capital Times. She joined the Cap Times in 2013 and has also covered Madison life, race relations, culture and music. She has also covered education and politics for the Oshkosh Northwestern.