During the tour, the senators saw border agents apprehend a woman who had climbed an 18-foot-tall bollard fence.
"You can read and you can study and you can talk but until you see things it doesn't become reality," said Schumer, who toured the border for the first time. "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."
President Barack Obama has urged Congress to pass immigration reform this year. While ceding the details of the negotiations to Congress thus far, the president has stepped to the forefront of the debate this week to prod lawmakers to finish work on the bill.
Border security also is critical to McCain, and other Republicans, who contend that some areas along the border are far from secure.
The senators' tour Wednesday by both ground and air allowed them to review manned and unmanned drones and different types of fences. They also watched as vehicles going to and from Mexico were scrutinized by border agents at the checkpoint in Nogales.
"In so many ways, whatever your views are on immigration, Arizona is ground zero," Schumer said. "What I learned today is we have adequate manpower, but not adequate technology."
With top Republicans and Democrats focused on the issue, immigration reform faces its best odds in years. The proposed legislation will likely install new criteria for border security, allow more high- and low-skilled workers to come to the U.S. and hold businesses to tougher standards on verifying their workers are in the country legally.
The bill is expected to be lengthy and cover numerous issues, including limiting family-based immigration to put a greater emphasis on skills and employment ties instead. McCain and Schumer promised the overhaul would pay for itself, while cautioning that their proposed border security package would be costly.
"Nobody is going to be totally happy with this legislation, no one will be because we have to make compromises," McCain said.
Bennet said the Gang of Eight has agreed to put border security before a path to citizenship, but are opposed to double-sided fences along the length of the U.S.-Mexico border. Some lawmakers in Arizona want more border fences.
"There is not one simple solution to the issue of border security," Bennet said. "This isn't as simple as someone on the East Coast saying 'We need a fence everywhere or we don't.' "
The senators stressed only comprehensive immigration reform, not piecemeal solutions, had any hope of passing both chambers of Congress.
"We are not going to slice it up," McCain said.
The legislation was initially promised in March. Immigration proponents have said the group needs to introduce legislation soon, while some Republican lawmakers complain the process has moved too quickly.
If passed, the legislation could usher in the most sweeping changes in immigration law in nearly 30 years.