Democratic Senate Candidates Lead in Ohio, Michigan and Wisconsin, Polls Find

Democratic Senate candidates in the Upper Midwest states of Michigan, Ohio and Wisconsin hold leads over their Republican competitors, keeping a narrow path open to maintaining Democratic control of Congress’s upper chamber next year, according to new New York Times/Siena College polls.

And, in a surprise that could shake up the Senate battlefield, Dan Osborn, a union organizer and industrial mechanic running as an independent, has jumped to a strong lead in Nebraska’s Second Congressional District, in and around Omaha, over the incumbent Republican, Senator Deb Fischer, reaching a level of support that could keep him competitive in the heavily Republican state.

The showing in the Midwest is a testament to the ability of Democrats, as well as Mr. Osborn, to separate the Senate contests from the presidential race, and keep control of the chamber in play. Senators Tammy Baldwin of Wisconsin and Sherrod Brown of Ohio, veteran incumbents, have created political brands that appear to be independent of their national party, while in Michigan, Representative Elissa Slotkin may be drafting on the strength of Democratic women in her state who occupy the posts of governor, attorney general and secretary of state.

In Ohio, Mr. Brown leads his Republican challenger, Bernie Moreno, 47 percent to 43 percent, drawing in 10 percent of voters that support former President Donald J. Trump and 13 percent of those self-identified as Republicans. Ms. Baldwin leads her Republican challenger, the banker Eric Hovde, 50 to 43, in Wisconsin, while Ms. Slotkin leads the former congressman Mike Rogers, 47 percent to 42 percent, in the race to succeed Michigan’s retiring Democratic senator, Debbie Stabenow.

The strong showing by Democratic Senate