WASHINGTON — A Republican critic of the Obama administration’s drone policy succeeded Wednesday in blocking a vote on John Brennan’s nomination to be CIA director over questions about the possible use of the unmanned weapons against American citizens.

Sen. Rand Paul, R-Ky., mounted a filibuster against President Barack Obama’s pick to lead the spy agency and he demanded that Obama or Attorney General Eric Holder issue a statement making clear that drones would not be used in the United States to kill terrorism suspects who are U.S. citizens.

Paul took the floor shortly before noon. With intermittent support from other conservatives holding similar views, plus Democratic Sen. Ron Wyden of Oregon, Paul spoke almost continuously for five hours before Majority Leader Harry Reid tried but failed to move to a vote on Brennan.

Paul resumed his oration, snacking on some candy at the dinner hour while continuing to speak. At one point, Sen. Mark Kirk, R-Ill, who walks haltingly with a cane because of a stroke, delivered a canister of hot tea and an apple to Paul’s desk, but a doorkeeper removed them.

Paul began speaking shortly before noon on what he said was the Obama administration’s refusal to rule out the possibility of drone strikes inside U.S. borders against American citizens. Sens. Mike Lee, R-Utah, Ted Cruz, R-Texas, Jerry Moran, R-Kan., Marco Rubio, R-Fla., and Ron Wyden, D-Ore., joined Paul several hours after he began speaking. Wyden has long pressed for greater oversight of the use of drones.

Paul said he would be willing to end his filibuster and proceed to a vote if he received the statement from the president or the attorney general. Holder came close to making such a statement earlier in the day during an exchange with Cruz at a Senate Judiciary Committee hearing, according to Paul.

Cruz asked Holder if the Constitution allowed the federal government to kill a U.S. citizen on U.S. soil who doesn’t pose an imminent threat. Holder said the situation was hypothetical, but that he did not think that in that situation the use of a drone or lethal force would be appropriate. Cruz criticized Holder for not simply saying “no” in response.

In a letter sent Tuesday to Paul, Brennan said the CIA does not have authority to conduct lethal operations inside the U.S.

Later in the evening Paul offered to allow a vote on Brennan if the Senate would vote on his resolution stating that the use of the unmanned, armed aircraft on U.S. soil against American citizens violates the Constitution. Democrats rejected the offer.

Despite the delays, Brennan’s bid to lead the spy agency received a boost when Sen. Lindsey Graham, R-S.C., said Wednesday that he is leaning toward voting for Brennan after receiving detailed information about the attack last September on the U.S. diplomatic mission in Benghazi, Libya.

Graham, along with Sen. John McCain, R-Ariz., had said they would oppose the nomination on the Senate floor if they didn’t get classified information detailing the Obama administration’s actions immediately following the attack that killed four Americans. Graham also criticized his GOP colleagues, calling the prospect of drones being used to kill people in the United States “ridiculous.”

“I think it’s paranoia between libertarians and the hard left that is unjustified,” Graham said. “I trust this president and other presidents to exercise commander-in-chief authority in a time of war.”

Holder told Paul in a March 4 letter that the federal government has not conducted such operations and has no intention of doing so. But Holder also wrote that he supposed it was possible under an “extraordinary circumstance” that the president would have no choice but to authorize the military to use lethal force inside U.S. borders. Holder cited the attacks at Pearl Harbor and on Sept. 11, 2001, as examples.

Paul said he did not dispute that the president has the authority to take swift and lethal action against an enemy that carried out a significant attack against the United States. But Paul said he was “alarmed” at how difficult it has been to get the administration to clearly define what qualifies as a legitimate target of a drone strike. “No president has the right to say he is judge, jury and executioner,” Paul said.

Brennan’s nomination won approval Tuesday by the Senate Intelligence Committee after the White House broke a lengthy impasse by agreeing to give lawmakers access to top-secret legal opinions justifying the use of lethal drone strikes against al-Qaida suspects overseas.