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Millions of dollars have been spent on campaign ads, but the race between Democrat Russ Feingold and Republican U.S. Sen. Ron Johnson remains the same.

Johnson has to make up ground to win a second term, according to Wednesday's Marquette University Law School Poll.

Feingold received support from 48% of registered voters while Johnson was backed by 41%. In the June survey, Feingold had a 4-point edge.

Among likely voters, Feingold's advantage narrowed from a month earlier when he held a 9-point advantage. Now, it's down to 5, with 49% backing the former three-term U.S. senator and 44% supporting Johnson.

"Looking at their favorables or their name recognition or the vote margin, there hasn't been a lot of change over the last month as both campaigns started to do a significant amount of advertising," poll director Charles Franklin said.

Franklin noted the race has narrowed since late 2015 and early 2016 when Feingold held double-digit leads.

In a three-way race, Libertarian candidate Phil Anderson drew 8% of registered voters, with Feingold at 45% and Johnson at 38%.

Feingold was viewed favorably by 40% and unfavorably by 32%, with 27% lacking an opinion. Johnson's favorable rating was at 34%, his unfavorable at 35%, with 32% having no opinion.

The Johnson and Feingold campaigns both saw good news in the poll.

"Sen. Feingold had a head start in this race, but everyone has always known this will be tight to the end and that Ron Johnson has the momentum," said Brian Reisinger, a Johnson spokesman. He added that the voters "fired" Feingold once, when Johnson beat him in 2010, and "we believe they'll do so again."

Michael Tyler, a spokesman for Russ Feingold, said, "despite $6 million in ads from Senator Johnson's corporate special interest friends, Russ continues to lead the race. We expect a competitive race, but one where voters choose Russ over Sen. Johnson and his big D.C. special interests."

Among leading politicians, President Barack Obama's job approval among registered voters stood at 51%, with 45% disapproval. House speaker Paul Ryan, a Republican from Janesville, had 48% job approval and 33% disapproval.

Gov. Scott Walker, who a year ago launched a failed bid for the Republican Party presidential nomination, continued to have trouble raising his ratings. Only 38% approved of how he's handling his job, while 58% disapproved.

Walker's job approval stood at about 50% before his re-election to a second term in 2014.

Franklin said that for Walker, the dramatic change in his approval ratings came in 2015 during the budget debate and the presidential race.

"And during almost all of the time since then his approval has been between 37% and 39% and disapproval of between 58% and 59%," Franklin said.

There was a slight tick up for Walker in March when 43% approved of the job he was doing. But that figure has since declined. Walker has said he is considering running for a third term in 2018.

On a policy issue, 59% agreed that marijuana should be legal and regulated like alcohol, while 39% disagreed. In September 2014, questioners were asked if the use of marijuana should be legal or illegal — 46% said it should be legal, while 51% said it should not be legal.

The poll of 801 registered voters was conducted Thursday through Sunday. For the full sample of voters, the margin of error was plus or minus 4.1%. Results for the 665 likely voters had a margin of error of plus or minus 4.5%.