Ben Wikler, the chairman of the Wisconsin Democratic Party, said he has seen an “explosion” in small-dollar donations and volunteers after the recent spate of controversial headlines from Johnson. While Wikler cautioned that it was impossible to predict the most viable candidates a year and a half away from the election, he said defeating the senator could send a “broader message.”

“My hope is that Ron Johnson runs and loses so spectacularly that Republicans rethink the extreme, fear-mongering, conspiracy-minded style of politics that has so scarred the country for the last four years,” Wikler said in an interview.

Sen. Gary Peters (D-Mich.), the new chair of the Democratic Senatorial Campaign Committee, doesn’t see incumbency as an advantage for Johnson, who called Peters a liar in December: “I just see Wisconsin as a really good opportunity for us to pick up a seat. And I don’t think it matters if it’s Sen. Johnson or somebody else that runs.”

Johnson scoffed at Democrats’ eagerness to face him, saying he “couldn’t care less what they think.” He brushed off questions about whether incumbency was an advantage in the race.