Dean’s Car Care, an auto repair shop in Portland, Ore., used to regularly rack up five stars and gushing accolades on Yelp and Google Reviews for its reliable and friendly service. “Honest and affordable. What else could you ask for?” one happy repeat customer wrote online in 2016. The reviewer said he had moved to a different part of the city, “but I still drive up to Dean’s whenever I need work done on my car or my truck.” That was then, before the owner, Marie Gluesenkamp Pérez, was elected to Congress last year as a Democrat, and became one of only a small number of lawmakers in her party who periodically crosses over to vote with Republicans. These days, Ms. Gluesenkamp Pérez is one of the most vulnerable Democrats in Congress, and Dean’s — the family business named for her husband — has become the target of vicious online trolling from the left. Progressives from around the country are review-bombing the establishment with posts expressing their ire at the first-term congresswoman for siding with Republicans on a bill to repeal President Biden’s student loan relief initiative.