“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. …

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.