Part of the answer is that Trump is trying to force Seoul to foot more of the bill for the U.S. military presence. But Seoul already pays half the U.S. costs and fields one of the largest armies in the world. Unlike Germany, it is no military deadbeat.
A likelier answer is that Trump sees American withdrawal as an achievement in its own right and hopes a peace treaty with the North is his ticket.
This is the kind of classic diplomatic blunder that, had it been committed by a Democratic president, would have produced thunderous denunciations from people like John Bolton and Mike Pompeo. Here’s an administration squeezing a close ally while telegraphing our negotiating terms to a deadly enemy. Expect Pyongyang to demand substantial U.S. withdrawals as its price for promises of peace and denuclearization. Beijing, which has long aimed to push the U.S. out of East Asia, will be thrilled.