...." Mike Pence’s schedule is so full of political events that Republicans joke that he is acting more like a second-term vice president hoping to clear the field than a No. 2 sworn in a little over six months ago. President Trump’s first term is ostensibly just warming up, but luminaries in his own party have begun what amounts to a shadow campaign for 2020 — as if the current occupant of 1600 Pennsylvania Avenue weren’t involved. The would-be candidates are cultivating some of the party’s most prominent donors, courting conservative interest groups and carefully enhancing their profiles. Mr. Trump...