Donald Trump and Hillary Clinton went head-to-head for the first time Monday night in a presidential debate at Hofstra University, moderated by NBC News’s Lester Holt.

Over the course of the evening, the candidates spent an inordinate amount of time on frivolous issues like Trump’s tax returns, who first pushed questions about Barack Obama’s birth certificate, and when Trump first said he opposed the Iraq War.

Here, you can weigh in on which substantive issue was the most important one discussed during the debate:

What was the key issue debated tonight?