Sen. Rand Paul declared victory Thursday after Attorney General Eric Holder assured him that the president cannot use a drone to kill a noncombatant American on U.S. soil -- an assurance Paul had sought during his 13-hour filibuster the day before.

"Hooray!" Paul responded when the letter was read to him for the first time during an interview with Fox News. "For 13 hours yesterday, we asked him that question, so there is a result and a victory. Under duress and under public humiliation, the White House will respond and do the right thing."

During his dramatic filibuster, which delayed a vote on CIA director nominee John Brennan, Paul had demanded the administration clarify the government's authority to kill on U.S. soil. The filibuster ended past midnight early Thursday morning. The Senate voted, 63-34, to confirm Brennan later Thursday afternoon.

Shortly before the vote, Holder sent a terse letter to Paul that read: "It has come to my attention that you have now asked an additional question: 'Does the President have the authority to use a weaponized drone to kill an American not engaged in combat on American soil?' The answer to that question is no."

In response, Paul said Thursday that "we're proud to announce that the president is not going to kill unarmed Americans on American soil." He later took to the floor to promote the attorney general's response, as the Senate moved to confirm Brennan.

Though Paul's 13-hour stand drew praise from all sides of the political spectrum, the senator also took heat Thursday from some in his own party who claimed he stirred unnecessary fear about the use of drones.

The senator "should know better," Sen. John McCain, R-Ariz., said, arguing that some of the concerns raised about drone missile attacks on Americans -- like Paul's suggestion that the U.S. could have killed Jane Fonda when she went to North Vietnam -- were "ridiculous."

Sen. Lindsey Graham, R-S.C., displayed a sign that showed the number of Americans killed in the U.S. by Al Qaeda -- 2,958 -- versus the number killed in the U.S. by drones, which is zero.

Paul, though, argued that he was raising concern about how future presidents might use their drone authority.

Paul told Fox News the critical senators "think the whole world is a battlefield, including America."

"I don't think the laws of war apply to America. I think the Bill of Rights do," Paul said.

While the Obama administration increasingly employs armed drones as a pivotal counterterrorism tool overseas, domestic law enforcement agencies are also moving to broaden the use of surveillance mini-drones over the next several years. The Federal Aviation Administration projects as many as 10,000 licensed systems by 2017.

The lethal drones used in Pakistan are a far cry from the unarmed eyes in the sky used in America. But Paul and a host of other lawmakers see constitutional pitfalls across the board -- namely focusing on how armed, and unarmed, drones might someday be used against American citizens.

Paul and the senators from both sides of the aisle who joined him on the floor Wednesday described a bleak future in which an unscrupulous government might use drones against its own population if left unchecked.

"Your notification is the buzz of propellers on the drone as it flies overhead in the seconds before you're killed. Is that what we really want from our government?" Paul asked.

Lawmakers have already started pushing legislation to rein in the drone program -- legislation that might get a second look after Paul's dramatic performance Wednesday.

Rep. Zoe Lofgren, D-Calif., and Ted Poe, R-Texas, last month introduced a bill to regulate domestic drones much like the government regulates wiretaps.

It would require officials to obtain a warrant in order to perform many kinds of surveillance with those drones. Further, it would prohibit law enforcement drones from being equipped with firearms or explosives in U.S. airspace.

"As we enter this uncharted world of drone technology, Congress must be proactive and establish boundaries for drone use that safeguard the constitutional rights of Americans," Poe said in a statement last month.

The use of armed drones in U.S. airspace fueled Paul's lengthy filibuster Wednesday. Before he took the floor, Paul announced that he had received a letter from Holder which opened the door, in extremely rare circumstances, to using a drone to kill someone within U.S. territory. Holder said "catastrophic" attacks such as the Sept. 11 attacks or the attack on Pearl Harbor are examples of circumstances where the president could conceivably feel such an action is necessary.

Testifying on Capitol Hill on Wednesday, Holder agreed that it would be unconstitutional to use a drone on American soil against a U.S. citizen or a suspected terrorist who did not pose an imminent threat.

Paul, during his filibuster, said he wanted a formal assurance from the administration that it would not use drones to kill noncombatant Americans, which prompted the Holder letter Thursday.

Aside from the legislation in the House, members of the Senate Intelligence Committee have floated the idea of establishing a sort of drone court to screen potential targets -- much like a court screens surveillance of foreign targets in the U.S.