Donald Trump’s presidency has all the stability of a flaming garbage truck careening down a mountain. Yet, somehow, he’s still behind the wheel, grinning like a maniac, while Democrats argue over the best way to file a noise complaint. His administration is a demolition derby in a fine china shop — tariffs, diplomatic blunders and economic upheaval. And yet, if the election were today, he’d probably win again. How is this happening? Divine retribution? A rip in the space-time continuum? Some elaborate karmic joke? No — it’s because, amazingly, Democrats have mastered the art of being simultaneously too cautious and...