The campaign still has three ugly months to go, but the odds — 83 percent odds, according to the New York Times’s model — are that it will end with the election of a sane, sensible president. So what should she do to boost America’s economy, which is doing better than most of the world but is still falling far short of where it should be?

There are, of course, many ways our economic policy could be improved. But the most important thing we need is sharply increased public investment in everything from energy to transportation to wastewater treatment.

How should we pay for this investment? We shouldn’t — not now, or any time soon. Right now there is an overwhelming case for more government borrowing.

Let me walk through this case, then address some of the usual objections.

First, we have obvious, pressing needs for public investment in many areas. In Washington, the aging Metro is in such bad shape that whole lines may have to be shut down for maintenance. In Florida, green slime infests beaches, in large part because failure to upgrade an 80-year-old dike or to purchase more land as a runoff area is forcing the Army Corps of Engineers to release polluted water from Lake Okeechobee. There are similar stories all across America.