The defeat last night by the House of Representatives of an amendment to the Department of Defense Appropriations Act that would have halted the National Security Agency’s program that collected phone records to monitor terrorist activity is causing many proponents of a strong national defense to heave a sigh of relief. The vote, which was allowed by Speaker John Boehner, was intended as a way for the House leadership to let its libertarian wing, led by Republican Justin Amash of Michigan, to blow off steam. Many members wanted to be able to go on record as opposing an unpopular measure that strikes many on the right as an extension of President Obama’s big government philosophy and tramples on the civil liberties of ordinary Americans. But with a majority of liberal Democrats joining Amash and 93 other Republicans, the attempt to spike a vital cog in the effort to defend the country against Islamist terrorists came within half a dozen votes of succeeding. If anything, Amash and others who, like Senator Rand Paul, want to drastically cut back on America’s commitment to engage with the world or to take a forward approach against security threats have good reason to be encouraged by the vote.

Though intended to head off just such an eventuality, the House’s actions may turn out to be a watershed moment in American politics. By coming this close to abolishing rather than just restraining the federal government’s efforts to monitor terrorist communications, Amash and his confederates are not just seeking to turn back the clock to September 10, 2001. They are also on the cusp of altering, perhaps for the foreseeable future, the national political alignment on national defense. The strength of GOP support for the ideas of Amash and Paul ought to scare Republicans for reasons relating to both principle and politics. Bu it should also worry Democrats like President Obama who, however reluctantly, has faced up to reality and rightly committed his administration to continuing most of his predecessor’s policies aimed at dealing with the terrorist threat. By choosing to either appease Amash, as Boehner has done, or to largely ignore it, as has been the position of the White House, the leadership of both parties is allowing the national mood to drift toward one in which the poorly reasoned libertarian critique of national defense policy has moved from the margins to the mainstream.

The reaction to the NSA metadata mining has largely been driven by fears that a national security state would be one that, as Senator Paul claimed during his filibuster earlier this year, might someday use a drone to kill an innocent American sitting in a Starbucks somewhere for no good reason. Unfortunately, this sort of fear-mongering has taken justified concerns about the administration’s penchant for increasing the power of the federal government and morphed it into something that bears little relation to fact. As advocates of the NSA program rightly stated during last night’s debate, this effort is neither unnecessary (it has been responsible for helping stop numerous terror attacks on the United States) nor has it been abused. Given that it has been conducted under close judicial scrutiny from a federal court and the intelligence committees of both the House and the Senate, the arguments that it is out of control or a threat to civil liberties is unjustified.

But, as was the case with Paul’s grandstanding on drones, the debate about the NSA is about something much bigger than one particular program. The willingness of Republicans like Amash to make common cause with leftists like John Conyers, who have always opposed virtually all national security measures especially those directed at Islamists, shows that the consensus within the party on defense has been toppled.

For decades, throughout the Cold War and into the first decade of the post-9/11 era, Republicans have been the party most dedicated to a strong national defense. That may have changed a bit last year as President Obama stole some of the GOP’s thunder by using the killing of Osama bin Laden as proof of his national security bona fides. But the basic split between most Democrats and most Republicans on these issues remained in place.

However, the ability of Amash and Paul to mobilize much of the GOP caucuses in both houses to support measures intended to hamstring national security efforts shows that a critical mass of Republicans have dropped their traditional posture on defense and adopted a position that bears an eerie resemblance to that of the far left. Isolationists of the left and right may be motivated by different factors. The left thinks America is always up to no good while their right-wing counterparts tend to act as if the country will only be safe if it seals itself off from the rest of the world. But as a practical matter, the two positions amount to the same thing.

This is a particular danger for Republicans since the notion that they can successfully compete in national elections as a party of isolationists against internationalist Democrats is a formula for political disaster. But whether or not it hurts their electoral prospects, responsible Republicans as well as Democrats who value the country’s future need to stop coddling or ignoring Amash and Paul and start fighting back against their campaign to take us back to 9/10. As Republican Rep. Tom Cotton said on the floor of the House last night, America is still at war, even if some in Congress would like to pretend that it isn’t. If that message continues to lose ground on Capitol Hill and in the public square, the price that the country will pay in blood may be high.