Last-minute revisions to security plans are being considered in Milwaukee, as former President Donald Trump reaffirmed on Sunday his plans to make his next campaign stop there for the Republication National Convention starting on Monday.

As Wisconsin officials touted robust preparation, a former U.S. Secret Service Agent and a former Secret Service liaison with a combined decades of experience urged any and all upcoming plans be revisited in light of the first assassination attempt of its kind in decades.

“Anytime something like this happens, it’s a security failure,” reacted Mike Olson, the former Secret Service Agent and now co-owner of private firm, 360 Security Services.

“Somebody didn’t do their job. Somebody failed,” echoed Ray Vin Zant, a former high-level U.S. Secret Service liaison in Minnesota.

During his career, Vin Zant ran security for former U.S. Senator Norm Coleman and arranged several presidential motorcades in Minnesota, including for former President George W. Bush.

“Any building that’s within sight range of the president is supposed to be protected,” he said.

“And here, we’ve got a building that was unprotected, and he was able to put a ladder up there — or however he got up there — and crawl up that roof and lay a sight on the president… One inch either direction, and he would have been dead.”

While questions swirl over how a gunman was able to access the former president on the campaign trail in Pennsylvania, pressure builds in Wisconsin where Trump is expected on Monday.

Wisconsin GOP Chairman Brian Schimming told journalists on Sunday he doesn’t expect much, if any, change to existing security plans.

“If they were to make any changes, there’d be a reason for it, but we don’t see a reason for it right now,” Schimming responded.

However, the head of a firm closely tied to those security plans earlier in the day confirmed anything remains on the table in terms of last-minute revisions.

Brian Dorow founded that private security firm, Secure Resources Unlimited. Formerly, he was also a Deputy Assistant Secretary of Homeland Security, appointed by Trump during his presidency.

Dorow said one factor involved in potentially revising and finalizing RNC security plans would be whether law enforcement ultimately determines the shooter acted alone, or if he was part of a larger plot that could be looking to make the next move.

“It’s time to really drill down overnight into the morning and see: Is there any tweaking that needs to take place? Is there any intel sharing that needs to take place? Is there any target-hardening that needs to take place?” he commented.

“The area around the RNC is safe. It’s secure, but again, based on more information coming forward, you have to be willing to pivot and then move in a different direction, and that’s certainly what will take place.”

RELATED: WISN: Waukesha-based security company partnering with RNC to keep event safe

President Joe Biden on Sunday said he ordered an independent review of how security was handled at the Pennsylvania rally. U.S. Secret Service will also review security plans for the upcoming RNC, he added.

Once federal and local investigations are completed, Olson said he expects Saturday’s political rally to serve as a tragic training scenario for years to come.

“Quite frankly, complacency kills — has a potential to kill, I mean,” he said.

“We don’t know enough yet about the individual that was involved in the shooting yesterday in Butler, Pennsylvania. But I would probably put money on it that at some point, we’re going to find out that he was on somebody’s radar. There was something known.”