But in 12 hours and 52 minutes, Sen. Rand Paul transformed himself from an outsider viewed with suspicion by much of his party to a unifying leader bringing together tea party voices with establishment Republicans and the Washington political elite. Paul’s voice, literally, was finally felt in Washington, and his colleagues were listening.

The Kentucky Republican’s decision to stand on the floor and launch the ninth-longest speech in the Senate’s history became a cause célèbre for Republicans hungry for a battle with the White House. Never mind that many of them, like Sens. John McCain and Lindsey Graham, rejected Paul’s chief contention — that the executive branch lacks the constitutional authority to unilaterally kill Americans on U.S. soil with unmanned drones — and several more were ready to confirm John Brennan to head the CIA.

( Also on POLITICO: Rand Paul pulls plug on nearly 13-hour filibuster)

On Thursday afternoon, Paulannounced he would relent and allow the Brennan vote to advance after receiving a letter from the Justice Department. Brennan was confirmed shortly afterwards, 63 to 34.

Supporting Paul — a tea party hero and conservative force — became a political plus for Republicans, who have struggled to unite since the November elections. One by one, GOP senators like Mitch McConnell of Kentucky, Marco Rubio of Florida, Pat Toomey of Pennsylvania, Ron Johnson of Wisconsin and John Thune of South Dakota came to the floor to talk in the libertarian’s defense, egged on by conservative and mainstream voices from the outside who urged them to “Stand with Rand.” Several conservative House members — like Texas Rep. Louie Gohmert and Michigan Rep. Justin Amash — showed up on the Senate floor just to lend moral support.

( PHOTOS: The senators who spoke during the filibuster)

“It seemed to be kind of spontaneous. People just started coming to the floor, first the other senators and then like 15 or 20 congressman came over, and that doesn’t happen very often, so we were pretty excited about that,” Paul told POLITICO.

The filibuster boomeranged on Twitter and throughout the conservative echo-chamber.

Close to midnight on Wednesday, Republican National Committee Chairman Reince Priebus tweeted that GOP senators should head to the floor to support Paul. The National Republican Senatorial Committee — once the scourge of the tea party — united with the far-right in praising Paul, even highlighting the senator’s filibuster in a fundraising push.

( WATCH: Rand Paul considering 2016 run)

McConnell — who only hours before was quietly negotiating a quick vote with Senate Majority Leader Harry Reid (D-Nev.) to confirm Brennan as early as Wednesday — came to the floor shortly before midnight to mount a defense of Paul and announce that he would vote to sustain the filibuster. It was another sign of how the tea party favorite has grown enormously influential with the GOP leader from his own state, particularly as McConnell tries to ward off any primary challenge in his 2014 reelection bid.

On Thursday, Paul was still the talk of the Senate, with his push reinvigorating Republicans looking for a way to recapture the Senate.

( PHOTOS: The longest filibusters in history)

“I think more than anything else a lot of this has to do with people just seeing him standing up, standing on principle, arguing for what he believes in and trying to get some answers from the administration,” Thune, No. 3 in Senate leadership, said in an interview. “I think the one thing that does unite us as a conference — irrespective of what our position may be on the underlying issue — is that the administration isn’t transparent.”

Toomey, who had just finished a two-hour dinner with President Barack Obama and a group of senators a couple miles down the road, returned to the Capitol late Wednesday night to defend Paul’s railing on the same president with whom he had just broken bread. He said in an interview Thursday morning that it all happened “spontaneously.”

“Once [Paul] got started, I think a lot of us felt that it’s a very important issue and it’s a very reasonable question,” Toomey, a former head of the conservative Club for Growth, said Thursday. “I feel like it’s important to support him because he’s doing the right thing.”

Sen. Mike Enzi, a soft-spoken Wyoming Republican in his third term, noted that the Kentucky firebrand “knows how to push the envelope.”

( WATCH: Rand Paul on drones: POLITICO’s full interview)

“Every one of us ought to be concerned about that,” Enzi said of the executive branch’s power to use drones. “It’s that inch-by-inch taking away our constitutional rights, giving people power used the wrong way easily.”

But despite the praise, hawkish Republicans like McCain and Graham were quick to criticize Paul on Thursday. Critics argued that the U.S. should do whatever it can to protect itself and the president was well within his constitutional rights to defend the country. And, they asked, where were these same GOP critics during the George W. Bush years, when the Republican president greatly expanded executive power during the war on terror?

“I just think that if the party believes that the drone program is illegal and that this president or any other president is going to use it to kill somebody in a café, who has done nothing, then I think the party’s lost its way,” Graham told POLITICO.

( WATCH: Rand Paul responds to McCain, Graham criticism)

Asked why he believed Republicans were quick to join Paul’s push, Graham — who himself is up for reelection in 2014 — said bluntly: “I just think it’s politics.”

Indeed, Paul said that “people on both the right and the left are supporting me. “We’ve got both Code Pink and Van jones, so I think we have a pretty good spectrum.”

He added that there’s now a “healthy debate” over the drones within the GOP, saying that “people are starting to understand that just by calling someone an enemy combatant doesn’t make them an enemy combatant. We have to assess their innocence.”

McCain was quick to dismiss Paul’s nearly 13-hour effort since other Republican senators also came to speechify, giving Paul a slight break, even if the Kentucky Republican was unable to excuse himself to even use the restroom.

“Usually, traditionally it’s been one person, makes it a lot easier if you have other people talking for him,” McCain said.

Republicans off Capitol Hill clearly were using Paul’s filibuster to their political advantage. It instantly galvanized the warring factions of the Republican Party in a fight against Obama, including the NRSC and the Tea Party Patriots, two groups that have been at odds in recent years over GOP candidates in Senate races. Both were quick to call on their supporters to unify behind Paul.

“People appreciate that someone is finally standing up and playing hardball with the president and his administration,” said Greg Mueller, a Republican strategist. “The party has been far too much seen as a party of capitulation and deal-making with a radically liberal president. Conservatives, tea party, mainstream Republicans want a fighting opposition party in Washington.”

Indeed, most Republicans were quick to unite behind that cause on Thursday, and McConnell even backed Paul on the policy question at the crux of the tea-party favorite’s push.

“The United States military no more has the right to kill a U.S. citizen on U.S. soil who is not a combatant with an armed unmanned aerial vehicle than it does with an M-16,” McConnell said on the floor. “The technology is beside the point. It simply doesn’t have that right and the administration should just answer the question.”

Democrats, too, were buzzing about Paul’s performance.

Hawaii Sen. Brian Schatz (D), who filled the seat of the late Sen. Daniel Inouye, was presiding over the chamber for much of Paul’s speech that went until the wee hours of Thursday.

“I consider it a healthy sign that when a member of the Senate brings up an issue simply by virtue of talking about it that he or she is able to attract [interest] to the issue and attract members to the Senate floor,” Schatz said. “That’s how the place ought to work.”

And Reid had his own impression of Paul’s effort.

“One thing I learned from my own experience with talking filibusters: to succeed, you need strong convictions but also a strong bladder, Reid said. “Sen. Paul has both.”

Jonathan Allen and Kate Nocera contributed to this report.