Interviews with New Jersey voters revealed that some Democrats’ breaks from their party last fall were neither flippant nor fleeting. Many described personal struggles to stress what they viewed as the needs of their family or community over partisanship. For some, mandates over vaccines and masks violated personal convictions over choices about their health that sparked fears about other potential invasions of privacy. Others expressed a newfound nuance to their political approach, prompted by faith in the party that has been shaken but not yet forsaken.

Democratic voters who have broken from their party over Covid often describe decisions they reached only after wrestling with issues such as their support for abortion rights and opposition to gun control—political positions that have constituted the core of the party for years…

Rachel Keane, a 35-year-old registered nurse and mother of two just outside the district in West Orange, N.J., said she had never voted Republican until last fall, when she opted for Mr. Ciattarelli and every other Republican candidate on her ballot. She worried about how her liberal parents would perceive her vote but described her decision as an awakening. She had always supported the party without a second thought, but her anger over the governor’s mask requirements for children made her question that loyalty.

“I knew I wasn’t going to vote for Murphy, but wasn’t sure if I was going to leave it blank or what,” she said. “Then I just got angry…And I voted Republican all the way down the line.”