Sen. Elizabeth Warren, campaigning in Iowa, was asked today why she didn’t support Sen. Bernie Sanders in the 2016 election if they were alike on policy issues.

Warren had decided not to run in the 2016 Democratic presidential primary and chose to endorse Hillary Clinton, the eventual nominee, over Sanders.

A woman in the audience at the event in Waterloo today asked Warren:

“Four years ago, I was in Des Moines, there were three national groups trying to get you to run then … and then Bernie ran. We thought, “Is there a difference between what you’re saying and what Bernie says. And if not, or if it’s not a big one, why didn’t you support him four years ago?”

Warren replied.

“I appreciate the question, and I appreciate that you wanted me to run four years ago. I get it. But I’m just going to be blunt with all of you, we can’t go back and re-litigate 2016. We just can’t. We just can’t.”

The Massachusetts senator was later asked by a reporter after the event to further distinguish herself from Sen. Sanders, now that both are in the 2020 race.

“Look, I’m going to get out and talk about the issues that pulled me into this race. It’s not up to me to describe anybody else’s position in the Democratic Party. The way I see it, I got plenty to talk about as it is about the structural change we need in this country and laying out how we can do this,” Warren said.