Sen. Rand Paul ended his day-long filibuster at 12:38 a.m. Thursday, almost 13 hours after he began speaking. The Kentucky Republican tried to stall a confirmation vote on CIA Director nominee John Brennan.

He took to the Senate floor at 11:47 a.m. ET.

And as a snowstorm swirled outside Wednesday in the nation's capital, Paul started his own Twitter hash tag that encapsulated his hours-long stand-off on Capitol Hill: #filiblizzard.

The Kentucky senator, known for his libertarian leanings, has sharply questioned the Obama administration's use of drones against American citizens overseas and vowed to speak Wednesday until he received more answers from the government about its policies. Brennan is considered one of the main architects of the drone program.

Paul in particular wants to know whether the government believes it has the authority to carry out drone attacks against American citizens on U.S. soil. He took issue with Attorney General Eric Holder's recent admission, in which he said he could envision a scenario where a drone strike would, in fact, be ordered against Americans on U.S. soil.

While Holder said it's never been done before and he could only see it in an extraordinary circumstance, Paul said he's disturbed by the idea that an American citizen would lose his or her rights while within the country's borders.

"I rise today to begin to filibuster John Brennan's nomination for the CIA," Paul said. "I will speak until I can no longer speak. I will speak as long as it takes."

Wearing a dark grey suit and a red tie, Paul detailed his argument, staring intently at the Senate leaders providing over the floor. The first-term senator stood with a thick binder full of notes in front of him -- but he rarely looked at them.

Paul, who hasn't ruled out a 2016 presidential bid, said he doesn't consider President Barack Obama is a "bad person," but he said the president is also "not a judge."

"He's a politician," Paul said. "He was elected by a majority, but the majority doesn't get to decide who we execute. We have a process for deciding this. We have courts for deciding this, to allow one man to accuse you in secret, you never get notified you have been accused."

He continued: "Your notification is the buzz of the propellers on the drone as it flies overhead in the seconds before you're killed."

Holder narrowed the list of those possible extraordinary circumstances Wednesday. In testimony before the Senate Judiciary Committee, Sen. Ted Cruz, R-Texas, pressed Holder whether he believed it would be constitutional to target an American terror suspect "sitting at a cafe" if the suspect didn't pose an imminent threat.

After first saying it would be "inappropriate," Holder attempted to clarify his answer by giving a firm "no."

But he also said the government has no intention of carrying out drone strikes inside the United States. Echoing what he said in a letter to Paul, he called the possibility of domestic drone strikes "entirely hypothetical."

Paul, who was elected in 2010 with wide tea party support, said he understands that due process doesn't apply to combat zones overseas.

"But when people say, 'Oh, the battlefield's come to America' and 'the battlefield's everywhere,' 'the war is limitless in time and scope,' be worried, because your rights will not exist if you call America a battlefield for all time," the senator said.

The term filibuster -- which originates from a Dutch word meaning "pirate" -- caught fire in the 1850s when it became a popular method to hold up a bill or vote on the Senate floor.

In the 1930s, Sen. Huey Long from Louisiana was known for reciting Shakespeare and reading recipes on the Senate floor when he filibustered. He once held the floor for 15 hours.

Former Sen. Strom Thurmond of South Carolina holds the record. He famously filibustered for 24 hours and 18 minutes against the Civil Rights Act of 1957.

In recent history, independent Sen. Bernie Sanders of Vermont held the floor in 2010 -- though technically not through a filibuster -- to protest a tax-cut deal for eight hours and 37 minutes.

Three hours in, Paul showed little signs of fatigue. He frequently shifted weight from one leg to the other and rested his hands on the desk from time to time. But a full glass of water sat untouched in front of him, and Paul rarely let go of his eye contact with his Senate colleagues.

After about six hours, however, Paul's level of fervor began to fade. The pace of his speech slowed down and he read more often from notes. Around 6:15 p.m. ET, he chowed down a snack in between sentences, talking with his mouth full.

For most of the time, Paul squarely placed blame on the president for what he perceived a dangerous precedent in federal law. The Kentucky senator was quick to make comparisons between President Obama and candidate Obama.

"I think it's also safe to say that Barack Obama of 2007 would be right down here with me arguing against this drone strike program if he were in the Senate," he said. "It amazes and disappoints me how much he has actually changed from what he once stood for."

Obama said there's something "contagious" about the office of presidency and cited the famous quote by John Dalberg-Acton.