When Pita Limjaroenrat was a student at Harvard in 2008, he shadowed his American classmates who were campaigning at the time for former President Barack Obama. The experience gave him a window into electoral politics, from phone banks and polling data to knocking on doors and putting campaign flags on front lawns.
Fifteen years later, Mr. Pita said he used what he learned in Massachusetts to help his recent campaign in Thailand, where he stunned the country’s political establishment by…