ATLANTA — Gov. Brian Kemp of Georgia easily dispatched Donald Trump’s hand-picked challenger on Tuesday in a Republican primary that demonstrated the limits of the former president and his conspiracy-fueled politics in a critical swing state. Kemp will face Democrat Stacey Abrams this fall in what will be one of the nation’s most consequential governor’s races. The GOP results, combined with the loss of the Trump-backed candidate for secretary of state, served as a stinging rebuke for the former president in a state he prioritized above almost all others.