Iowa’s Republican Gov. Terry Branstad was finally confirmed on Monday to be Donald Trump’s ambassador to China, and he announced that he would resign on Wednesday. Branstad’s two non-consecutive tenures as governor from 1983 to 1999 and again from 2011 to 2017 add up to 8,169 days in office, or over 22 years, making him the longest-serving governor of any state in American history. GOP Lt. Gov. Kim Reynolds will assume office following Branstad’s resignation, and the state’s first woman governor subsequently will face election to a full term in 2018. Reynolds has yet to formally clarify her intentions for 2018, but she is expected to run.

If Reynolds does decide to run for election in her own right, she’ll have history on her side. Geoffrey Skelley of the University of Virginia’s Center for Politics recently conducted an extensive analysis of how every governor since World War II who took office after a vacancy has fared if they ran in the next election. ...