To see how far Rand Paul has gotten in his project to inject libertarianism into a GOP foreign policy debate long dominated by neoconservatives and other interventionists, think back to what official Republicanism looked like only 27 months ago.

Then, just one month before a new and different-sounding Tea Party wave of freshmen politicians (including Paul) flooded into Capitol Hill talking about cutting rather than limiting the growth of government, Weekly Standard founder William Kristol, American Enterprise Institute President Arthur Brooks, and Heritage Foundation President Ed Feulner took to the pages of The Wall Street Journal to fire a shot across the whippersnappers' bow: Don't you even think about cutting defense, kids.

The military "is neither the true source of our fiscal woes, nor an appropriate target for indiscriminate budget-slashing in a still-dangerous world," the Three Amigos of the Establishment wrote. "Anyone seeking to restore our fiscal health should look at entitlements first, not across-the-board cuts aimed at our men and women in uniform."

Even as recently as 10 months ago, Feulner et al were keeping House Republicans in line by praising the proposed budget of Rep. Paul Ryan (R-Wisconsin) for its "partial restoration of national defense as the No. 1 priority of the federal government." While "many would like to see American military spending restored more rapidly," they wrote, "Ryan's budget is a choice about our future, and this is a time to choose—not hide behind the sequestration process."

Fast-forward to February 2013, and even Paul Ryan is saying "the sequester is happening," which means that the defense budget will likely take a $55 billion (or 9 percent) cut by the end of this month.

And Rand Paul? He's giving a major speech on "restoring the Founders' vision of foreign policy" tomorrow at Ed Feulner's old stomping grounds, the Heritage Foundation. Which is now headed up by Rand Paul's good friend Jim DeMint, the recently resigned senator from South Carolina who has lately been talking a lot about pruning back America's overseas commitments while saying nice things about Rand's Establishment-reviled father Ron.

That the Republican and national conversations have shifted so much in such a short time is partly a testament to both Pauls, and their often-lonely long game of re-introducing skepticism about America's forward thrust into the world and re-tethering the commander in chief to the Constitution. But where Ron Paul breaks through the soft interventionist consensus with bracing and sometimes abrasive blasts of convention-defying, anti-imperial purism—witness his Tweet yesterday about murdered Navy SEAL sniper Chris Kyle dying "by the sword"—Rand Paul (who reacted to Kyle's killing by telling Breitbart.com that "Chris Kyle was a hero like all Americans who don the uniform to defend our country") has figured out a way to sell anti-neoconservative ideas to audiences allergic to his father.  

What will that approach look like in practice tomorrow at Heritage? Going by a pre-speech interview with The American Conservative's Daniel Larison, Paul's foreign policy vision will focus less on the "blowback" his father constantly warns about, and more on the "process" of restoring congressional participation in the constitutional balance of power over military affairs. Instead of getting to the immediate "no" on interventionism abroad, whether in Mali or Syria or Iran, this focus on congressional oversight allows Paul to work more slowly toward the same likely conclusion, while allowing for coalition building and stressing a certain epistemological humility.

"If you get to that, then you'll get to the facts ultimately," he told Larison. "It's hard to always comment on every set of facts in the world, particularly if we're not engaged in the debate."

Some of Ron Paul's biggest fans detect in such words a worrying openness to intervention, and willingness to play ball with the same neoconservative establishment Rand railed against in his first book. This suspicion is only heightened when he utters such crowd-pleasing silliness as "any attack on Israel will be treated as an attack on the United States."

But 27 months ago, there was no Republican in the United States Senate proposing to repeal the notorious 9/14 authorization of force that has in effect given the president a blank check to send assassination drones all over the globe. Few senators of either party spend so much time tilting at the windmill of Fourth Amendment restoration in an age of ubiquitous government spying. In an era when it's never been easier for disgruntled citizens to route around legislators who ignore their wishes, Rand Paul stands uniquely positioned to exploit the vast gap between America's instinctive foreign policy modesty and its governing consensus to the contrary.

"I've been one of the few Republicans who have supported coming home from Afghanistan," Paul told Larison, "and it's actually been remarkable how opinions have changed not only in the country, but in the Republican Party. Four years ago or three years ago even, you had Republicans talking about staying forever. You still have some, but you had many talking about staying forever and many saying that if you believed in any timeline for coming home you were a cut-and-run coward....I think it's remarkable that even many of those Republicans have given up on that."

The new wave of Republican non-interventionists is still massively outnumbered by the old guard. Freshman Sen. Ted Cruz (R-Texas) brought out some of the longest knives in the GOP's confirmation ambush of squishy foreign-policy realist and occasional Israel critic Chuck Hagel, calling into question Rand's hopeful insistence that the Tea Party's "stated principles prevent it from being brought into the neoconservative fold." The sequester may yet be pushed back again.

But by insinuating himself successfully into the heart of the GOP, Rand Paul is doing more than mainstreaming libertarian-flavored foreign policy: He is forcing the purist, and therefore theoretical, instincts of his father's coalition to come into contact with the messy business of broad political persuasion. He will lose those along the way who prefer to lob rhetorical anti-imperial grenades from the margins. But he—and the country—stand to gain a whole lot more.