Sen. Rand Paul's filibuster will inevitably fail at its immediate objective: derailing John Brennan's nomination to run the CIA. But as it stretches into its sixth hour, it's already accomplished something far more significant: raising political alarm over the extraordinary breadth of the legal claims that undergird the boundless, 11-plus-year "war on terrorism."

The Kentucky Republican's delaying tactic started over one rather narrow slice of that war: the Obama administration's equivocation on whether it believes it has the legal authority to order a drone strike on an American citizen, in the United States. Paul recognized outright that he would ultimately lose his fight to block Brennan, the White House counterterrorism chief and architect of much of the administration's targeted-killing efforts.

But as his time on the Senate floor went on, Paul went much further. He called into question aspects of the war on terrorism that a typically bellicose Congress rarely questions, and most often defends, often demagogically so. More astonishingly, Paul's filibuster became such a spectacle that he got hawkish senators to join him.

"When people talk about a 'battlefield America'," Paul said, around hour four, Americans should "realize they're telling you your Bill of Rights don't apply." That is a consequence of the September 2001 Authorization to Use Military Force that did not bound a war against al-Qaida to specific areas of the planet. "We can't have perpetual war. We can't have a war with no temporal limits," Paul said.

This is actually something of a radical proposition. When House Republicans attempted to revisit the far-reaching authorization in 2011, chief Pentagon attorney Jeh Johnson conveyed the Obama administration's objections. Of course, many, many Republicans have been content with what the Bush administration used to call a "Long War" with no foreseeable or obvious end. And shortly before leaving office in December, Johnson himself objected to a perpetual war, but did so gingerly, and only after arguing that the government had the power to hold detainees from that war even after that war someday ends.

Paul sometimes seemed to object to the specific platform of drones used against Americans more than it did the platform-independent subject of targeted killing. But Paul actually centered his long monologue on the expansive legal claims implied by targeting Americans for due-process-free execution: "If you get on a kill list, it's kind of hard to complain.... If you're accused of a crime, I guess that's it.... I don't want a politician deciding my innocence or guilt." Paul threw in criticisms of other aspects of the war on terrorism beyond targeted killing, from widespread surveillance of Americans to the abuses of state/Homeland Security intelligence "fusion centers."

Paul also name-checked several bloggers, reporters and think-tankers critical of targeted killing, like The Guardian's Glenn Greenwald, Firedoglake's Kevin Gosztola, The Atlantic's Conor Friedersdorf, and the Council on Foreign Relations' Micah Zenko. At one point, he read from one of my Danger Room articles, and another from Danger Room editor/founder Noah Shachtman. And Paul's filibuster reached unlikely advocates over Twitter, from X frontwoman Exene Cervenka to former baseball slugger Jose Canseco.

All this may be unsurprising coming from one of the Senate's premiere civil libertarians. But as the filibuster picked up more and more media attention – and especially social-media attention – hawkish senators began joining in. Sen. Marco Rubio (R-Florida) praised Paul's efforts at compelling transparency from the White House. What Paul is arguing is "no less important than our Constitutional government itself," said Sen. John Cornyn (R-Texas), no dove.

It would be foolish to presume that Paul's moment in the spotlight heralds a new Senate willingness to roll back the expanses of the post-9/11 security apparatus. Rubio, for instance, stopped short of endorsing any of Paul's substantive criticisms of the war. But Paul did manage to shift what political scientists call the Overton Window – the acceptable center of gravity of discussion. Rep. Mike Rogers (R-Michigan), the hawkish chairman of the House intelligence committee, put out a statement that started out subliminally criticizing Paul but ultimately backing him on the central point.

"It would be unconstitutional for the U.S. military or intelligence services to conduct lethal counterterrorism operations in the United States against U.S. citizens," Rogers said. "And as Chairman of the House Intelligence Committee, I would never allow such operations to occur on my watch. I urge the Administration to clarify this point immediately so Congress can return to its pressing oversight responsibilities."

Again, that's still a long way from substantively constraining an executive branch that's enjoyed both widespread latitude and congressional deference since 9/11. But Paul's filibuster posed a challenge to the Senate more than it does Brennan or President Obama. "Is perpetual war OK with everybody?" he asked.