It has been 50 years since historian Richard Hofstadter named the peculiar strain of American politics that allows for otherwise mainstream politicians to veer into conspiracy theories. He called it "the paranoid style" because no other word "adequately evokes the sense of heated exaggeration, suspiciousness and conspiratorial fantasy that I have in mind."

For those who do politics in the paranoid style to gain traction, however, there has to be a critical mass of voters willing to buy what they're selling. This, frankly, has never been a problem in a republic founded on individual liberty, deep suspicion about government, and a strange fascination with the occult.

There was proof of that this week when the current torchbearer of the paranoid tradition, Rand Paul, the Republican senator from Kentucky, temporarily brought several surveillance methods used by the National Security Agency and Federal Bureau of Investigation to a halt by blocking the extension of the provisions of the U.S. Patriot Act that authorized them. This made Mr. Paul a hero among "liberty lovers," Silicon Valley geeks and all those who think President Barack Obama is listening in on their calls.

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The NSA's bulk collection of U.S. phone records has generated a fierce debate about the balance between civil liberties and national security ever since Edward Snowden revealed the program in 2013. Mr. Obama and a majority in Congress had agreed that the program, adopted in the wake of the 2001 terrorist attacks, should be scaled back, and legislation to make phone companies responsible for storing their records passed the House of Representatives in May. That bill requires the NSA to seek a warrant from a special court to access the records.

The House bill was supposed to pass the Senate before the June 1 expiration of the Patriot Act provisions. But Mr. Paul used a procedural tool to stop the Senate from voting on the bill and made a nearly 11-hour speech long on paranoid-style rhetoric. "Little by little, we've allowed our freedom to slip away," he said during his marathon soliloquy.

Even Mr. Obama agreed it was a bad idea to let the Patriot Act authorizations expire without having an alternative in place; the White House warned it could hamper investigations into terrorist activities. That Mr. Paul was willing to run that risk raises questions about his fitness for the 2016 Republican presidential nomination, which he aims to win by appealing to libertarians.

During his Senate speech, Mr. Paul's campaign was sending out fundraising tweets and hawking wares, including one that read: "The NSA knows I bought this Rand Paul T-shirt."

Mr. Paul's stunt outraged his upper-chamber colleagues, to whom he responded, "Some of them, I think, secretly want there to be an attack on the United States so they can blame it on me." He later walked back that comment, saying "hyperbole" got the better of him "in the heat of the battle."

The problem is, this was far from an isolated outburst. It's the way Mr. Paul usually does politics.

On right-wing Newsmax TV on Monday, Mr. Paul said people "don't want the President looking at their phone records. … They don't trust the President. This is the President who used the [Internal Revenue Service] against Tea Party groups" and "to invade our religious liberty."

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Mr. Paul raises some important points about privacy in an age when it seems to be under siege from all sides. It has earned him a flock of devoted young followers in such unlikely (for a Kentucky Republican) places as San Francisco, where he last month drew wild applause with his stump-speech standard, "What you do on your phone is none of the government's damn business."

But his penchant for paranoid rhetoric routinely undermines his message. Earlier this year, when he argued for parental choice in the debate about vaccinations, he added that he knew of "many tragic cases" of "children who wound up with severe mental disorders after vaccines."

Mr. Paul's odds of winning the Republican nomination remain slim. And Arizona Senator John McCain, the party's 2008 nominee, calls him "the worst candidate we could put forward." But Mr. Paul's popularity among factions in the party risks making it more difficult for whoever gets the nomination to win their votes in a general election. He has branded most of his opponents as apologists for the "Washington machine that gobbles up our freedoms and invades every nook and cranny of our lives."

Call it paranoid. Or, as Mr. McCain sees it, just "wacko."