Bangladesh, Aug. 9 -- The political movement that propelled Donald Trump to the White House twice has entered what may be its most consequential phase yet-not because of pressure from Democrats or establishment Republicans, but because of a growing rebellion from within its own ranks. What was once a relatively unified “Make America Great Again” (MAGA) coalition is increasingly divided over the future of the movement and the role of Trump himself.

For years, Trump and MAGA were treated as inseparable. To support one was to support the other. Today, however, a new faction argues that the movement has outgrown its founder. Its members insist they remain committed to MAGAs original principles but believe Trump has departed from ...