Grover Cleveland is the historical standard among American presidents who lose or leave office then seek to regain it. The reason is simple: he achieved his goal. Cleveland, however, is hardly the only commander-in-chief who tried to win back what was lost. The difference is that the historical record for ex-presidents trying for a comeback is pretty terrible. And there are some Democrats who, toward the end of Cleveland’s second term in the late 1880s, wished Uncle Jumbo had stayed retired from politics — a cautionary tale for former President Donald Trump and his Republicans. In the waning d…