Wall Street and the business community, breaking from a yearslong trend, are hedging their political bets by making more contributions to Democrats in the midterm elections, according to fundraising data compiled by the nonpartisan Center for Responsive Politics.

Not since 2008 have donors in the securities and investment industry given a higher percentage to Democratic candidates and party committees than to Republicans, the data show. This year through Oct. 17, Wall Street contributors donated about $85 million to Democrats...