We need to make America great again, and for that Donald Trump might be our man. For all the anxiety the White House has caused, brewing constitutional crises at home and anger abroad, Mr. Trump has opened a path to reunify this politically divided nation. A “team of rivals” that transcends party lines, composed of eminent men and women, could rein in the administration. This bipartisan group, preferably endorsed by past U.S. presidents, would be made up of former cabinet members and heads of independent federal agencies. Inspired by the British Shadow Cabinet, it would be structured to mirror the...