Somehow Elaine Quijano, the moderator, found time for not one but two questions inspired by the Committee for a Responsible Federal Budget — an organization concerned that despite relatively low budget deficits now and extremely low borrowing costs, the federal government may face fiscal problems a couple of decades down the line. There may be something to this, although not as much as deficit scolds claim (and Ms. Quijano managed to suggest that Mrs. Clinton’s proposals, which are fully paid for, are no better than Mr. Trump’s multitrillion-dollar debt blowout).

But if we’re worried about the longer-term implications of current policies, the buildup of greenhouse gases is a much bigger deal than the accumulation of low-interest debt. It’s bizarre to talk about the latter but not the former.