WASHINGTON -- Sen. Rand Paul (R-Ky.) announced on the Senate floor Wednesday he intended to filibuster the nomination of John Brennan as director of the CIA, citing concerns about President Barack Obama's policy on civil liberties.

"I will speak until I can no longer speak," Paul said.

Paul, an outspoken libertarian, pointed to what he called the abuses of executive power and civil liberties under Obama's administration. In particular, he objected to the contents of a letter he received from Attorney General Eric Holder that asserted the U.S. government had the legal authority to kill a U.S. citizen on American soil.

"Where is the Barack Obama of 2007?" he asked, referring to then-presidential candidate Obama's criticism of Bush-era violations of civil liberties. "If there were an ounce of courage in this body, I would be joined by many other senators," he added. "Are we going to give up our rights to politicians?"

Paul had asked the Justice Department about the constitutionality of drone strikes and whether they could be used agains U.S. citizens. Holder responded in a letter that conceded the military could authorize a drone strike on U.S. soil.

"It is possible, I suppose, to imagine an extraordinary circumstance in which it would be necessary and appropriate under the Constitution and applicable laws of the United States for the President to authorize the military to use lethal force within the territory of the United States," Holder wrote.

Paul elaborated on his concern Wednesday: "When I asked the president, 'Can you kill an American on American soil,' it should have been an easy answer. It’s an easy question. It should have been a resounding an unequivocal, ‘No.’ The president’s response? He hasn’t killed anyone yet. We’re supposed to be comforted by that. The president says, ‘I haven’t killed anyone yet.’ He goes on to say, ‘And I have no intention of killing Americans. But I might.’ Is that enough? Are we satisfied by that?"

Paul started his filibuster speech around 11:45 a.m. Unlike most modern filibusters, the Kentucky senator is actually attempting to talk through the whole thing -- like Jimmy Stewart in "Mr. Smith Goes To Washington" -- rather than simply raising his hand to object and requiring 60 votes to proceed. The last "talking" filibuster was in 2010, when Sen. Bernie Sanders (I-Vt.), spoke out against extending the Bush-era tax cuts. Filibuster reform advocates have proposed returning to this old-fashioned style.

"I will not sit quietly and let him shred the constitution," Paul said of Obama, later adding that getting an answer from the president on drone strikes was like "pulling teeth."

The White House declined to comment Wednesday.

Paul's speech drew on the work of bloggers from both the left and right who have criticized the president on civil liberties, such as Glenn Greenwald of The Guardian and Conor Friedersdorf of The Atlantic. Kevin Williamson of the National Review also earned a mention for a piece he wrote asking whether under Obama's standards the Nixon and Johnson administrations should have bombed college campuses.

"To be bombed in your sleep? There's nothing American about that," Paul said. "There's nothing constitutional about that."

Last week, Paul voted for the nomination of Chuck Hagel as defense secretary -- another key Obama national security appointment -- after first voting against cloture on the matter, saying he was using his vote to try to get more information about Hagel.

Brennan's confirmation was expected as soon as Wednesday, according to a Senate Democratic leadership aide. Following Paul's filibuster, the aide was still "cautiously optimistic" that once the senator ended his speech a time agreement for a vote could be reached.

Paul also used his filibuster Wednesday to speak out against the wars in Afghanistan and Iraq. He conceded that he would have supported the Afghanistan war at the outset, but said it had since become far wider than its initial response to the Sept. 11 attacks.

"The problem is as this war has dragged on, they take that authorization of use of force to mean pretty much anything, and so they have now said that the war has no geographic limitations," he said. "So it's really not a war in Afghanistan, it's a war in Yemen, Somalia, Mali. It's a war in unlimited places."

Paul went on to reprimand Congress for ceding its authority to govern U.S. wars. "Were we a body that cared about our prerogative to declare war, we would take that power back," he said. "But I'll tell you how poor -- and this is on both sides of the aisle -- how poor is our understanding or belief in retaining that power here."

WATCH: Paul's filibuster live on CSPAN-2.

This is a developing story. Updates will appear below:

Sen. Mike Lee (R-Utah) joined the filibuster just before 3 p.m., giving Paul a break after more than three hours of speaking.

Sen. Ted Cruz (R-Texas) then took over for Lee just after 3:10 p.m. "You must surely be making Jimmy Stewart smile," he said.

Paul resumed speaking around 3:45 p.m, and the filibuster went bipartisan just before 4:00 pm, when Sen. Ron Wyden (D-Ore.) joined in.

Wyden said he intended to vote for Brennan's confirmation, but added that the nomination provided an opportunity to seek more information on the Obama administration's legal documentation for targeted killings. He said the Senate Intelligence Committee had gotten that information.

Sen. Marco Rubio (R-Fla.) came to the Senate floor to ask a question of Paul just before 4:20 p.m. Rubio did not criticize the administration's targeted-killings policy per se, but he defended the Senate's right to ask questions of presidential appointment nominees.

Sen. Saxby Chambliss (R-Ga.) joined the filibuster just before 4:40 p.m. The Georgia senator, who is retiring in 2014, said that he thought the administration should be capturing and interrogating more suspected militants, rather than launching drone strikes at them. He said that he did not support the nomination of John Brennan.

Senate Majority Leader Harry Reid (D-Nev.) took to the floor at about 4:45 p.m. to try to invoke cloture on the Brennan nomination to allow the vote to happen Wednesday night.

Sen. Paul (R-Ky.) said he would be happy to vote, but that he hasn't gotten the answer he wanted, and therefore objected to holding the vote.

The filibuster showed no signs of stopping as it entered its eighth hour Wednesday evening. Sen. Ted Cruz (R-Texas) read aloud supportive tweets.

"I think the technical term for what the Twitterverse is doing right now is called 'blowing up,'" he said.

Meanwhile, Obama and several Republican senators were dining at the Jefferson Hotel, meeting in an attempt to find a replacement plan for the automatic spending cuts that took effect March 1.

Just after 9:15 p.m., Sen. John Barrasso (R-Wyo.) joined the filibuster as it neared 10 hours.

Close to 11:30 p.m., Sen. John Thune (R-S.D.) took to the Senate floor, followed by Senate Minority Leader Mitch McConnell (R-Ky.). McConnell expressed support for Paul's efforts, and said that he would not support Brennan's nomination if Reid invoked cloture.

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    This video frame grab provided by Senate Television shows Sen. Rand Paul, R-Ky. speaking on the floor of the Senate on Capitol Hill in Washington, Wednesday, March 6, 2013. Senate Democrats pushed Wednesday for speedy confirmation of John Brennan's nomination to be CIA director but ran into a snag after a Paul began a lengthy speech over the legality of potential drone strikes on U.S. soil. But Paul stalled the chamber to start what he called a filibuster of Brennan's nomination. Paul's remarks were centered on what he said was the Obama administration's refusal to rule out the possibility of drone strikes inside the United States against American citizens. (AP Photo/Senate Television)

  • Rand Paul

    This video frame grab provided by Senate Television shows Sen. Rand Paul, R-Ky. speaking on the floor of the Senate on Capitol Hill in Washington, Wednesday, March 6, 2013. Senate Democrats pushed Wednesday for speedy confirmation of John Brennan's nomination to be CIA director but ran into a snag after a Paul began a lengthy speech over the legality of potential drone strikes on U.S. soil. But Paul stalled the chamber to start what he called a filibuster of Brennan's nomination. Paul's remarks were centered on what he said was the Obama administration's refusal to rule out the possibility of drone strikes inside the United States against American citizens. (AP Photo/Senate Television)

  • Rand Paul Leads Senate Filibuster Against Brennan Vote

    WASHINGTON, DC - MARCH 06: U.S. Sen. Rand Paul (R-KY) is seen on TV monitors as he participates in a filibuster on the Senate floor March 6, 2013 on Capitol Hill in Washington, DC. Sen. Paul was filibustering the Senate to oppose the nomination of John Brennan to be the next director of CIA. (Photo by Alex Wong/Getty Images)

  • Rand Paul Leads Senate Filibuster Against Brennan Vote

    WASHINGTON, DC - MARCH 06: U.S. Sen. Rand Paul (R-KY) is seen on a TV monitor participating in a filibuster on the Senate floor as Politco reporter Tim Mak works on his story at the Senate Press Gallery March 6, 2013 on Capitol Hill in Washington, DC. Sen. Paul was filibustering the Senate to oppose the nomination of John Brennan to be the next director of CIA. (Photo by Alex Wong/Getty Images)

  • Rand Paul Leads Senate Filibuster Against Brennan Vote

    WASHINGTON, DC - MARCH 06: U.S. Sen. Rand Paul (R-KY) is seen on a TV monitor as he participates in a filibuster on the Senate floor March 6, 2013 on Capitol Hill in Washington, DC. Paul is filibustering the Senate to oppose the nomination of John Brennan to be the next director of CIA. (Photo by Alex Wong/Getty Images)