Egads! After a disastrous first 100 days, Donald Trump is starting to have a much more successful presidency. This is not what we, his foam-at-the-mouth critics, had planned or perhaps secretly hoped for. Some of this is a function of good policy, like getting NATO’s European members and Canada to spend much more on their defense, something previous American presidents asked for, but much too politely. Far from destroying the Atlantic alliance, as his critics feared, Trump may wind up being remembered for reviving and rebalancing it, to the advantage of both sides. Some of this is courageous policy: Joining...