Four senators working on an immigration bill got a first-hand look at the challenges – and, perhaps, the successes – of securing the nation’s border with Mexico on Wednesday.

During a tour of border control measures in Nogales, Ariz., the foursome saw a woman successfully scale an 18-foot fence, according to an account provided by Sen. John McCain (R-Ariz.) on Twitter. McCain attached a photo of himself and Sen. Charles Schumer (D-N.Y.) on the tour, though the woman was not visible in the shot.

“Border Patrol successfully apprehended her, but incident is another reminder that threats to our border security are real,” McCain wrote in a follow-up tweet two minutes later.

The senators, including Jeff Flake (R-Ariz.) and Michael Bennet (D-Colo.), were on the tour as part of their work on an eight-member bipartisan group that is developing legislation that would overhaul the nation’s immigration laws. Republicans have called for stricter border control measures as part of the bill, a provision that could be tied to a path to citizenship for the nation’s 11 million illegal immigrants.

The Obama administration has said it supports increased enforcement efforts, but White House officials have pointed to a significant increase in resources and sharp drops in border crossings as evidence that measures added in recent years have paid dividends.

“I’ve seen it many times before,” McCain said, when asked during a news conference about the woman climbing the fence. “One of the sad things about all this is that mostly people who jump over the fence are doing that because they want a better life and I understand that. We try to separate the drug cartels from individuals who are simply trying to cross over so they can improve their lives, but at the same time we have to have a legal way of doing that.”

The senators said they are studying increases in surveillance technology that would reduce the need for more roads and border control agents.

“What I learned was that we have adequate manpower, but we don’t have adequate technology,” Schumer said.