Usually, the quadrennial nominating conventions are opportunities for both major political parties to unite their base around their respective nominee ahead of the general election. But former President Donald Trump’s speech at the Republican National Convention has one former Republican sounding the alarm about what he believes are significant cognitive issues plaguing the ex-president. In his latest essay for the Atlantic, U.S. Naval War College professor emeritus Tom Nichols — who was a Republican until 2016 — voiced his concerns about the mental fortitude of the 45th president of the Unite…