ASTON, Pa. — Donald Trump said Thursday that he would make lower college tuition a priority in his administration, his most extensive remarks to date on college affordability, an issue that Hillary Clinton has made central to her pitch to millennial voters.

Addressing a rally here, the GOP nominee said that universities should use their tax-free "multibillion-dollar endowments" to help students with tuition and debt, but that instead too many sit on the funds or invest them.

“Instead these universities use the money to pay their administrators, to put donors names on their buildings, or just store the money, keep it and invest it. In fact, many universities spend more on private-equity fund managers than on tuition programs,” he said. “But they should be using the money on students, for tuition, for student life and for student housing. That's what it's supposed to be for.”

Trump said that he would work with Congress to encourage universities to lower tuition costs — or risk losing federal tax breaks. But he offered few other specifics Thursday night.

“The students are choking on those loans. They can't pay them back. Before they start, they're in trouble. And it's something I hear more and more and it's one of the things I hear more than anything else,” he said.

Clinton has put forward a detailed plan to make public colleges and universities tuition-free for students in families earning up to $125,000 a year and to make the college years debt-free for all students. She also promises to help students refinance existing debts at more favorable interest rates. Her campaign has created an online “calculator” so students can see how much they would save under her proposals.

The college affordability plan is a key part of Clinton’s recently stepped-up appeal to millennials. During a speech at Temple University in Philadelphia this week aimed at young voters, she lamented that “as you know better than most, tuition keeps going through the roof and debt keeps piling up.”

During that speech, Clinton gave a shout-out to Sen. Bernie Sanders of Vermont, the runner-up in the Democratic primaries, with whom she collaborated on her current college affordability plan. Sanders routinely outperformed Clinton among voters under 30 during the primaries and caucuses.

A political committee supporting Clinton, Correct the Record, characterized Trump’s college-affordability remarks as an empty gesture.

“Trump introduced what appeared to be an attempt at a college affordability proposal, which is ironic coming from the man behind the student-swindling Trump University and Trump Institute,” a statement from the group said.