By THÉRÈSE MARGOLIS     U.S. President Donald J. Trump’s penchant for political reversals is now considered par for the course in his topsy-turvy White House, but his abrupt about-face on Washington’s membership in the multinational trade Trans-Pacific Partnership (TPP) last week was definitely a doozy. After having lambasted the pact throughout his political campaign, denouncing its potential impact on the U.S.