... Wall Street’s disdain for the bottom-up populist campaigns of Senators Elizabeth Warren of Massachusetts and Bernie Sanders of Vermont has gotten a lot of attention. The candidates’ full-throated attacks on corporate greed, extreme wealth and banking excesses are backed up by ambitious plans to upend the industry’s everyday operations. Wariness extends far beyond an elite financial fellowship, though, to many small and medium-size businesses whose executives are not reflexively Republican but worry that the ascendancy of a left-wing Democrat would create an anti-business climate. In their view, sweeping plans to remake the health care system or slash the cost...