Sen. Rand Paul (R-Ky.) had what will probably be the defining moment of his presidential campaign on Sunday night. It could conceivably help him, but at a high political cost. It could also end his presidential hopes.

The junior senator from Kentucky infuriated his Republican colleagues by blocking a vote on the USA Freedom Act, a bill that would curtail a controversial National Security Agency bulk phone-data collection program and reauthorize three other surveillance programs that expired at midnight. The NSA had stopped collecting telephone metadata Sunday afternoon, when it became clear no deal would be finalized in time. It won't be able to resume until the Senate acts, the House approves any changes, and President Obama signs the bill.

In Rand Paul's telling, and that of the red-shirted "Stand With Rand" supporters who filled the Senate gallery on Sunday evening, Paul stuck a shiv in the government surveillance state, at least for a few days. "The Patriot Act will expire — it will expire tonight," Paul said on his way out of the Senate chamber Sunday night. "The point I wanted to make is that we can still catch terrorists using the Constitution."

Paul had some other help, if inadvertent. Senate Republicans, notably Majority Leader Mitch McConnell (Ky.), had wanted to extend the USA Patriot Act as is. They fell short. Then, after a week's recess, when it became clear the votes just weren't there for the Patriot Act renewal, McConnell reluctantly agreed to put the "flawed" USA Freedom Act up for a last-minute vote on Sunday, and the Senate agreed, 77 to 17. The bill had passed the House on May 13, 338-88, and Obama supports it.

Senate GOP hawks say the Freedom Act puts too many constraints on the NSA; Paul and some other civil libertarians say it still goes too far. But his usual civil-liberty allies in the Senate signaled their comfort with the House bill, leaving Rand Paul the lone holdout. In the Senate, that's often enough to delay a bill, and Paul did so on Sunday.

Whether or not it was his prime motivation, as Sens. Dianne Feinstein (D-Calif.) and John McCain (R-Ariz.) suggest, Paul will earn a lot of money for his presidential campaign. But his chances of becoming the 2016 Republican nominee just went from unlikely to long-shot.

Shutting down American espionage and surveillance capabilities, even for a few days, is too off-brand for the GOP — especially at the moment.

Paul is "a niche candidate of a shrinking niche, because events are not playing out the way he anticipated two years ago when he began running for president," George Will said on Fox News Sunday. "The world looks much more dangerous than it did," and "literally cashing in" on his "conscientiousness as a libertarian" really "muddies the waters" of his intentions.

In a crowded Republican presidential field, Rand Paul is betting he can monopolize the libertarian caucus. It's a gamble. Forcing expiration of the NSA provisions for a couple of days was a small victory on its own. But "his larger political victory was that he took ownership of Patriot Act opposition," said David Weigel at Bloomberg Politics, "angering Republican colleagues whom he is happy to anger."

Weigel names McCain and Sen. Lindsey Graham (R-S.C.), but Paul also angered McConnell, who has endorsed him for president, and Senate Intelligence Committee Chairman Richard Burr (R-N.C.), who vowed on Sunday that "there won't be any negotiations with Rand Paul from this point forward." Paul didn't attend the GOP caucus meeting before Sunday's session, and Republicans walked out on him en masse when he started speaking.

The big question for Paul is whether there are enough civil libertarians in the Republican Party, and if so, whether they will vote in the primary. Plenty voted for his father, former Rep. Ron Paul (R-Texas), but it wasn't enough.

"People here in town think I'm making a huge mistake," Rand Paul said Sunday evening. "Some of them I think secretly want there to be an attack on the United States so they can blame it on me."

In other words, Rand Paul sounds like a lot of Democrats after the Sept. 11, 2001, terrorist attacks. That wasn't a good place to be, politically.

Brit Hume at Fox News hammered the same point on Sunday. Paul "seems confused about which party he's running in," he said. "There's a segment of the Republican electorate which shares his somewhat paranoid views of things, and he'll have their support, but that's not a nominating set."

Rand Paul seems to know the risks, and he seems content to go down swinging. And if he does stake his political future on curtailing government spying and lose, unlike other GOP presidential contenders, he probably shouldn't expect a soft landing at Fox News.