Michigan U.S. Senate candidate John James, a Republican, says he made a "terrible error" in allowing his first campaign ad of the general election in Michigan to air with brief footage of what appears to be a swastika. James held an impromptu press conference after a Monday night debate against incumbent Democrat Debbie Stabenow, telling reporters and supporters alike, "I need to fess up."

"I was taught by excellent leaders, the best of which being my mom and dad, to do the right thing even when it's hard," said James. "We should have caught this error, and we didn't and there is no excuse."

The ad, which has since been pulled down from YouTube, includes footage of a school hallway with a bulletin board full papers -- one of which appears to be printed with a swastika symbol, commonly associated with the rise of Nazi Germany and most recently, the white nationalist movement. Twitter users, however, re-posted the ad and showed screen grabs of the hallway.

See John James’ TV ad featuring a Nazi swastika for yourself on his YouTube channel: https://t.co/SCC2ATCmdi - it’s :11 in here (or watch vid clip here). Disgusting #misen pic.twitter.com/NCAX7kQTjo — 𝙂𝙧𝙖𝙝𝙖𝙢 𝘿𝙖𝙫𝙞𝙨 (@grahamdavis) October 15, 2018

The Republican businessman, who earned the support of President Trump after his primary election, said that the image was part of stock footage for the ad and was unaware of its origins. He noted, however, "I'm not making any excuse."

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"It's my responsibility to stand and denounce hatred and bigotry and take responsibility for that error and omission," said James.

James said at his press conference that the ad in question was already being "phased out nationally" and a new ad would be rolling out in its place on Tuesday, this one focusing on the candidate's father.

James said he takes responsibility for everything that his campaign team "does and fails to do" and vowed to do "everything in my power to make sure this never, ever happens again."

He added, slamming Democratic opponent Sen. Debbie Stabenow in the process, "I love everyone and I denounce hatred and bigotry in all its forms. But this is also indication that our message is working."

"This is also an indication of how low people are willing to go to take a message like this and to imply that a combat veteran, somebody who would put his life on the line for American values...doesn't belong to one party or the other, but belongs to Americans." James added that the blowback shows how Stabenow will "say and do anything to get re-elected."

The president has since doubled-down on his support for James, calling the candidate a "star" in a tweet on Tuesday.

WOW, John James is making headway in Michigan. We are bringing jobs back to the State, and the People of Michigan appreciate it. Debbie Stabenow has been no help, if anything, a major hindrance. John James is a star, I hope the voters see it. Polls are tightening! — Donald J. Trump (@realDonaldTrump) October 16, 2018

"We are bringing jobs back to the State, and the People of Michigan appreciate it. Debbie Stabenow has been no help, if anything, a major hindrance," he added.