The Fourth Amendment to the Constitution of the United States protects American citizens from "unreasonable searches and seizures" and requires "probable cause" to obtain a warrant for such searches. But there are two places where the Fourth Amendment doesn't apply, even for U.S. citizens, and that's at border crossings and airports. Now, according to an investigation by NBC News, U.S. Customs and Border Protection (CBP) officials are seriously ramping up efforts to take advantage of that fact.

In fact, data provided by the Department of Homeland Security to NBC showed that searches of cellphones by border agents have exploded, growing fivefold in just one year, from fewer than 5,000 in 2015 to nearly 25,000 in 2016. Moreover, 2017 is expected to be a blockbuster year with 5,000 devices searched in February alone, more than in all of 2015.

"That's shocking," said Mary Ellen Callahan, former chief privacy officer at the Department of Homeland Security. She wrote the rules and restrictions on how CBP should conduct electronic searches back in 2009. "That [increase] was clearly a conscious strategy, that's not happenstance." "This really puts at risk both the security and liberty of the American people," said Senator Ron Wyden, D-Oregon. "Law abiding Americans are being caught up in this digital dragnet." "This is just going to grow and grow and grow," said Senator Wyden. "There's tremendous potential for abuse here."

One such example came from a Buffalo, New York couple, Akram Shibly and Kelly McCormick, who were detained by U.S. Customs & Border Protection officers upon their return to the U.S. after a trip to Toronto on Jan. 1, 2017. According to NBC, officers held the couple for two hours, took their cellphones and demanded their passwords.

"It just felt like a gross violation of our rights," said Shibly, a 23-year-old filmmaker born and raised in New York. But he and McCormick complied, and their phones were searched. Three days later, they returned from another trip to Canada and were stopped again by CBP. "One of the officers calls out to me and says, 'Hey, give me your phone,'" recalled Shibly. "And I said, 'No, because I already went through this.'" The officer asked a second time.. Within seconds, he was surrounded: one man held his legs, another squeezed his throat from behind. A third reached into his pocket, pulling out his phone. McCormick watched her boyfriend's face turn red as the officer's chokehold tightened.

And while the left will undoubtedly link this recent surge in cell phone searches to the 'racist' Trump administration, the fact is that the practice began a decade ago, late in the George W. Bush administration, and really ramped up in the last two years of the Obama administration following domestic terrorist attacks in Orlando and San Bernadino.

But since current border search policies were written in 2009, legal advocates argue that several court cases have set new precedents that could make some CBP electronic searches illegal.

Several former DHS officials pointed to a 2014 Supreme Court ruling in Riley v California that determined law enforcement needed a warrant to search electronic devices when a person is being arrested. The court ruled unanimously, and Chief Justice John Roberts wrote the opinion. "Modern cellphones are not just another technological convenience. With all they contain and all they may reveal, they hold for many Americans 'the privacies of life,'" wrote Roberts. "The fact that technology now allows an individual to carry such information in his hand does not make the information any less worthy of the protection for which the Founders fought." Because that case happened outside of the border context, however, CBP lawyers have repeatedly asserted in court that the ruling does not apply to border searches.

Meanwhile, Senator Ron Wyden (D-OR) says that as early as next week he plans to propose a bill that would require CBP to at least obtain a warrant to search the electronics of U.S. citizens, and explicitly prevent officers from demanding passwords. "The old rules ... seem to be on the way to being tossed in the garbage can," said Senator Wyden. "I think it is time to update the law."