Republican candidate for California governor Travis Allen asked a brutal personal question during a debate of the frontrunner, Democratic Lt. Gov. Gavin Newsom, about an affair the California Democrat had in 2005.

"The question is very simple ladies and gentlemen: if you can't trust Gavin with his best friend's wife, how can you trust him with your state?" Allen asked.

Candidate for California governor Travis Allen (R) asks front runner Gavin Newsom (D) the toughest question of the NBC Bay Area SVCF debate. pic.twitter.com/R96T2g8Lq8 — Scott McGrew (@ScottMcGrew) May 9, 2018

Allen was referring to an affair Newsom had with Ruby Rippey Gibney, who was Newsom's commission appointments secretary. Rippey Gibney was married to Newsom's campaign manager and friend Alex Tourk.

Newsom responded to the question by bringing up President Donald Trump.

"It's hard with respect to hear from Mr. Allen who is a devout supporter of Donald Trump talk about the issue of sexual harassment," Newsom said to applause.

"And as it relates to the issue that's been referred to, I was honest about it. I was open about it. I apologized for it. I was wrong, and I learned an enormous amount from it. And I'm a much better person as a consequence," he said.

Due to the unique top-two jungle primary system in California, voters will vote on all candidates to determine who will be on the ballot in the general election. The top two candidates coming out of the June 5 primary, regardless of party, will face off in the November election.

Fellow Democrats in the race have also criticized Newsom for his affair.

Democratic gubernatorial candidate Amanda Renteria, who previously served as the political director of Hillary Clinton's 2016 presidential campaign, went after Newsom in a series of tweets. She accused Newsom of sexual misconduct and "misusing his power."