As Debbie Mucarsel-Powell revved up the Democratic faithful in a restaurant named for Thomas Edison, she was looking for a little electricity in her campaign to unseat Senator Rick Scott of Florida.

So she turned the attention of the crowd at Edison’s Lab Restaurant and Bar in Fort Myers, where the inventor had a winter estate and laboratory, to the abortion referendum in Florida that could decide the fate of her bid.

“The man has never run in a presidential election when our voters turn out,” she said of Mr. Scott. Perhaps more important, she added to the boisterous crowd, “he has never run against the millions of women and men that are ready to come out to the ballot box to protect reproductive freedom.”

Ms. Mucarsel-Powell, a former medical school dean who was swept into the U.S. House by the 2018 blue wave, and then swept right back out two years later, is an underdog. Mr. Scott, a wealthy fixture of Florida politics who served for eight years as governor, has the high ground in the red-tinted state as he seeks his second term in the Senate.

But she has one thing on her side: Floridians will be deciding by referendum whether to overturn the state’s unpopular six-week abortion ban.

Beyond Florida, Senate candidates from across the political spectrum in Missouri, Montana, Nevada, Nebraska, Maryland and Arizona will appear on the ballot alongside measures to protect abortion rights. The track record of such measures, which have passed everywhere they have been introduced since the Supreme Court overturned Roe v. Wade in 2022, would seem to bode well for candidates who support them.