Trump was much better last night, and the debate opened up follow-on lines of attack on Biden, most importantly on oil. Still, it’s frustrating to see how many points Trump leaves on the table by simply not knowing his own brief. Take health care. I think it’s political malpractice that the White House doesn’t have some sort of Obamacare replacement plan, which would neuter all the “you don’t have a plan” attacks he gets all the time. But that aside, if you ask the White House about health care, it will send you a raft of materials on the policies it has pursued to lower health-care costs. Trump doesn’t have to have all this memorized. He doesn’t have to be a health-care wonk. All he needs is about five points or so that he can routinely throw out there when asked about this, rather than simply promising a big, beautiful replacement plan at a later date, which he did again last night. Trump famously operates on his instincts. He’d be in a stronger position right now if one of his instincts was to master enough details to make the best possible case for himself, especially in high-profile, perhaps campaign-defining settings.