The NBC host faced online backlash after failing to press Donald Trump on his claim that he opposed the Iraq War in 2002.

Hillary Clinton and Donald Trump sat down Wednesday for their first joint-candidate event of the general election, and in the end, it was moderator Matt Lauer who faced the most Twitter backlash.

The NBC host spoke with both candidates during the forum, in which they covered topics of national security and the military with questions fielded by Lauer and a live audience comprising active-duty service members and veterans.

Lauer started by asking them both about "the most important characteristic that a commander-in-chief can possess" and military policies in general, but focused more on Clinton's email scandal and failed to press Trump on his claim that he opposed the Iraq War. 

See some of the reactions below. 

WTF is the matter with Matt Lauer not calling @realDonaldTrump out on his lie about not supporting going into Iraq. MSM keep him honest!!!

— Rob Reiner (@robreiner) September 8, 2016

. @mattyglesias: Matt Lauer totally blew it on Trump’s blatant lying about Iraq and Libya https://t.co/DsRbubnarP

— Arianna Huffington (@ariannahuff) September 8, 2016

If only @MLauer had access to this crack team of journalists. https://t.co/DYtkFFNrB8

— Matthew Yglesias (@mattyglesias) September 8, 2016

I don't blame Lauer for asking the email question. But it's ABSURD that he started off with Trump, "Why should you be Commander-in-Chief?"

— Jon Favreau (@jonfavs) September 8, 2016

Matt Lauer, getting ready for the #NBCNewsForum tonight. pic.twitter.com/sMHI1afiOy

— Wil Wheaton (@wilw) September 8, 2016

Shoutout to Matt Lauer for not asking a follow up when Trump lies a out opposing Iraq war. Maybe Matt was still thinking about emails.

— Wil Wheaton (@wilw) September 8, 2016

Precisely. What an embarrassment. What a travesty. We will remember this, NBC and @mlauer. You are responsible. https://t.co/WESVMoK0d3

— Jeff Jarvis (@jeffjarvis) September 8, 2016

OK great @Mlauer call, quoting a Trump tweet about how rape is the natural consequence of having women in the military. No followup

— Joan Walsh (@joanwalsh) September 8, 2016

So @MLauer’s plan is just to let Trump lie about his past statements on Iraq?

— Matthew Yglesias (@mattyglesias) September 8, 2016

Trump is lying about what he said on Iraq and Lauer just lets it go by. Lauer did four follow ups on email.

— Jon Lovett (@jonlovett) September 8, 2016