Wisconsin voters prefer likely Democratic presidential nominee Hillary Clinton over presumptive GOP nominee Donald Trump. That's according to the results of the most recent Marquette University Law School poll, which showed the former secretary of state leading the celebrity real estate developer 42 percent to 35. The gap jumps to 46 to 37 among likely voters.

Marquette pollster Charles Franklin said Clinton's lead among likely voters may be larger because some Republicans say they won't vote for Trump.

"What we're seeing at the moment is some decline in Republican certainty of voting and a little bit of an increase on the Democratic side," he said.

The number of Republicans who said they will definitely vote in November dropped 9 percentage points since March while voter enthusiasm grew 3 percent for Democrats.

Walker's Approval

The survey released Wednesday also found that Gov. Scott Walker's job approval rating has taken a slide to 39 percent, down from 43 percent in March just before Wisconsin's presidential primary.

Walker's approval rating first fell below 40 percent nearly a year ago, just before he dropped out of the Republican race for president.

Walker, who is spending this week on a trade mission to Mexico, was asked about the Marquette Poll during a conference call with reporters. In addition to his own low approval rating, the survey showed people hold somewhat negative views of the state budget and Wisconsin's economy.

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"When I do listening sessions, I hear actually good things," Walker said. "I think the reason the polls are that way is because of the media. The headlines are always about negative and bad things, so it's no wonder that people would feel that way in the polls."

Marquette Pollster Charles Franklin said people viewed the budget and the economy favorably during Walker's reelection bid in 2014, but that changed when Walker introduced his last budget in early 2015.

"And none of those numbers has sharply turned around," Franklin said. "Things are fairly negative, and until we get a new budget proposal next February, I don't know that voters will tune into these things in ways that could bring about change."

U.S. Senate Rematch

In other elections-related findings, the rematch race for one of Wisconsin's U.S. Senate seats between Democrat Russ Feingold and Republican incumbent Ron Johnson has continued to tighten. Feingold now leads Johnson 45 percent to 41, slightly narrower than his 47-42 edge in March and much closer than the 12-point gap he had in February.

Feingold appears to have more breathing room among likely voters however, leading Johnson by 9 percent, 51-42.

"That's in part because of the likelihood of turnout falling off among Republicans," Franklin said.

The Marquette Law School Poll was conducted Thursday through Sunday, sampling 800 registered Wisconsin voters. It has a margin of error of plus or minus 4.4 points.

Editor's Note: This story has been updated with additional reporting including comments from Scott Walker and Charles Franklin.