Sen. Rand Paul (R–Ky.) said yesterday he'll oppose the confirmation of William Barr, who President Donald Trump has nominated to be the next attorney general.

"I'm a no," Paul told Politico yesterday. "He's been the chief advocate for warrantless surveillance of U.S. citizens. I think that the Fourth Amendment should protect your phone calls and your bank information. People shouldn't be allowed to look at it without a warrant."

It's valid criticism. As the American Civil Liberties Union noted last month, Barr helped oversee a secret phone surveillance program when he led the Justice Department during the George H.W. Bush administration. For years, the feds collected phone records on calls made between people in the U.S. and those in countries connected to alleged drug trafficking activities. (For more on Barr's drug war, read Reason Senior Editor Jacob Sullum's column from December.)

This program would serve as a sort of precursor to the National Security Agency surveillance enabled by the PATRIOT Act following the 9/11 terror attacks. And while Barr was no longer working in the federal government by the time the PATRIOT Act was implemented, he still defended the program, which civil liberties advocates believe violated the Fourth Amendment's protections against warrantless searches. Testifying before the House Intelligence Committee in 2003, Barr even suggested the PATRIOT Act didn't go far enough.

Paul, for his part, has always been uneasy regarding Barr's nomination. "I'm concerned that he's been a big supporter of the PATRIOT Act, which lowered the standard for spying on Americans," the Kentucky Republican told Meet the Press in December. "And he even went so far as to say, you know, the PATRIOT Act was pretty good, but we should go much further."

"I can tell you, the first things that I've learned about him being for more surveillance of Americans is very, very troubling, Paul added.

Ultimately, Paul's opposition likely won't mean very much. Republicans hold a 53-47 majority in the Senate, and it's hard to imagine that two other GOP senators will betray their party and vote no. Also, Alabama Democratic Sen. Doug Jones has already said he will vote to confirm Barr. The full Senate will likely vote on the nomination this week, according to Politico.

Bonus link: Paul has long been one of the Senate's most ardent critics of the PATRIOT Act. Here he is discussing that issue and others with Reason's Matt Welch in 2015: