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McCain Tweets that he witnessed woman scaling Ariz.-Mexico border fence

@SenJohnMcCain on Twitter

Four members of the "gang of eight" senators pushing for a bipartisan approach to immigration reform on Wednesday got an unexpected optical to demonstrate their case: During a tour of the Arizona-Mexico border, Sen. John McCain, R-Ariz., wrote on Twitter, they witnessed a woman in Nogales, Ariz., "successfully climb an 18-ft bollard fence a few yards away from us."

McCain, who was joined by Sens. Chuck Schumer, D-N.Y., Jeff Flake, R-Ariz., and Michael Bennet, D-Colo., on the tour guided by U.S. customs and border control, included an image (left) with his Twitter post that showed him standing with Schumer and a handful of border patrol agents before the steel fence.

"Border Patrol successfully apprehended her, but incident is another reminder that threats to our border security are real," McCain wrote in a separate post.

It's an area that's been something of a sticking point on an issue that both parties largely agree warrants reform. Generally, Democrats have called for a path to citizenship for the 11 million undocumented immigrants currently residing in the United States; many Republicans, though, have insisted that tightened border security should be a prerequisite for any other type of action.

Schumer addressed the incident with reporters following the tour.

"You can read and you can study and you can talk but until you see things it doesn't become reality," he said, according to the Associated Press. "I'll be able to explain this to my colleagues. Many of my colleagues say, 'Why do we need to do anything more on the border?' and we do. We should do more."