AT TUESDAY’S presidential debate, both candidates pledged to shower money on struggling college students.

Mitt Romney praised a tuition-free college fund in Massachusetts and promised to “keep our Pell Grant program growing,” a theme he also struck this month when he pledged not to cut “funding” and “grants” for college students. President Obama responded he has already enlarged Pell, the $36 billion keystone of the federal student aid system, by billions over his first term. One reason to raise tax revenue, the president said, is to keep investing in education and other priorities.

Neither candidate mentioned that Pell grants already face a looming funding crisis. They certainly offered no sense of how they would deal with that shortfall and keep growing awards. (Disclosure: The Washington Post Co.’s education division includes Kaplan University, whose students use federal aid to finance their course work.)

Mr. Obama doubled Pell funding in part by reforming the federal student loan system and applying the savings to Pell. But Congress didn’t commit enough revenue to keep Pell grants at their more generous terms permanently. Last year Mr. Obama and Congress scrambled for last-minute cash to maintain the pumped-up program. Another scramble is in the offing once that is exhausted. The New America Foundation’s Jason Delisle points out that Mr. Obama proposed some stopgap Pell funding in his last budget but only enough to see the program through one more year, setting up another funding cliff.

Mr. Romney’s positioning is even more suspect. The Republican had previously argued that federal education spending fuels the rise in tuition, making his latest statement appear to be just another general-election flip to the middle. Even were that not the case, any spending pledge from a candidate whose most consistent and specific priority is to cut taxes should be automatically suspect. How would Mr. Romney pay for his “growing” program, given that he says he won’t raise revenue but will close the deficit? He didn’t say on Tuesday, and neither did a Romney campaign spokesperson we contacted.

In May Mr. Romney proposed to “refocus” grant dollars, which probably means adjusting the program’s eligibility requirements, cutting some students out. That could save some cash, but he gave no details. Paul Ryan, Mr. Romney’s running mate, has proposed specific money-saving changes to Pell, including a freeze on the size of awards. But Mr. Romney’s insistence that he would grow Pell awards indicates he isn’t on board with Mr. Ryan’s austerity, at least for the moment.

Fine promises on Pell grants without the substance to back them up neither serve Pell-dependent students nor advance smart budgeting, in which priorities compete fairly and tradeoffs aren’t hidden.