Former Fed Governor Daniel Tarullo on Thursday said the turmoil in the crucial short-term lending market in September raises a fundamental question for regulators — will the new rules put in place in the wake of the 2008 financial crisis exacerbate an “over-hoarding” of capital during market stress?

In the September crisis, interest rates on short-term “repo” loans spiked to 10% from under 2%, setting off alarm bells on Wall Street and in Washington.