*Editor's note: This story has been updated to reflect a fundraising email that Beto O'Rourke sent in response to the ad.

A Republican super PAC has started airing a TV ad invoking Beto O'Rourke's 1998 drunk-driving arrest, a significant escalation in the air war against the Democratic candidate for U.S. Senate with less than a week until Election Day.

In the commercial, the group, ESAFund, seizes on a Washington Post fact check of the El Paso congressman's claim during a September debate that he "did not try to leave the scene of the accident." The Post gave O'Rourke "Four Pinnochios" for the statement, pointing to a police report from the time that cited a witness saying he attempted to flee.

"What's worse — driving drunk or lying about it?" a narrator asks in the 30-second spot, which starts with footage of an unrelated car accident, then goes over the fact check and ends with O'Rourke's mugshot. "Beto O'Rourke put Texas lives at risk — and he doesn't deserve your vote."

With less than a week to go, ESAFund goes on TV with @BetoORourke's 1998 DWI arrest: "Beto O'Rourke put Texas lives at risk, and he doesn't deserve your vote." Seen tonight on KPRC in Houston: pic.twitter.com/JizA32jvHO — Patrick Svitek (@PatrickSvitek) November 1, 2018

The fact check was controversial due to the conflicting accounts about whether he tried to leave the scene, and O'Rourke later asserted that the "police report on this count is wrong."

"I reached out to the passenger who was in the car that I was driving — who also does not appear in the police report, among other factual errors — somebody that I’ve not spoken to in more than 15 years, and asked her recollection of that evening," O'Rourke said during an interview at the Texas Tribune Festival in September. "She said, 'No, we were in the median of the road. We did not try to flee. I don’t know that there was anywhere we could have gone.'"

According to reports, O'Rourke was arrested at the scene and charged with driving while intoxicated but went on to complete a court-approved diversion program, and the charges were dropped. He has since spoken openly about the episode as an inexcusable mistake, though the alleged attempt to flee has not surfaced until his current campaign.

The ad is being backed by a six-figure buy in the Houston area, according to the president of ESAFund, Brian Baker. Earlier Wednesday, the group disclosed to the Federal Election Commission that it had unloaded $636,000 against O'Rourke, most of it on media placement.

O'Rourke's campaign did not respond to a message seeking comment on the ad. But on Thursday afternoon, the campaign launched a $3.5 million online fundraising drive in response to the commercial, calling it the "most despicable attack ad yet" and claiming Cruz allies were "running scared" amid a tightening race.

ESAFund, formerly known as the Ending Spending Action Fund, joined the Senate race early last month when it dropped over $1 million on a TV ad buy featuring a spot attacking O'Rourke as a "Democrat under the influence of Nancy Pelosi," the House minority leader. At the time, it was not entirely clear who was funding the super PAC due to FEC deadlines; subsequent reports show that it has received $3.5 million from three donors: Las Vegas casino mogul Sheldon Adelson and his wife, Miriam, as well as another GOP megadonor, Marlene Ricketts.

ESAFund is one of four super PACs that have racked up seven-figure investments in the Senate race, the biggest player being the pro-Cruz group Texans Are. Three of the four super PACs are on Cruz's side, while the other — Texas Forever, the most recent entrant in the race — is benefitting O'Rourke.

Such groups can raise and spend unlimited amounts of money as long as they do not coordinate with campaigns.