There are several credible candidates in Ohio’s Republican primary to replace Sen. Rob Portman next year. With so many options for voters, deciding which to rule out first seems like a smart first step. Contenders include former state treasurer and legislator Josh Mandel, former Ohio GOP chairwoman Jane Timken, Cleveland-area businessmen Bernie Moreno and Mike Gibbons, and Cincinnati venture capitalist J.D. Vance. Most polls have shown upwards of a third of likely voters are undecided, with Mandel in the lead, Vance trailing behind him, and everyone else laboring in single digits. Donald Trump won Ohio by 8 points last November,...