Rand Paul's foreign policy grew up. In a major speech in New York last week, Paul laid out a case for conservative realism. "We need a foreign policy that recognizes our limits and preserves our might, a common-sense conservative realism of strength and action. We can't retreat from the world, but we can't remake it in our own image either," he said.

Zack Beauchamp at Vox called it one of the most important foreign policy speeches in decades, saying that if Paul runs in 2016 "he isn't going to move toward the Republican foreign policy consensus; he's going to run at it, with a battering ram."

Paul's vision of "limits" is a far cry from George W. Bush's second inaugural, where the president declaimed, "By our efforts, we have lit a fire as well — a fire in the minds of men. It warms those who feel its power, it burns those who fight its progress, and one day this untamed fire of freedom will reach the darkest corners of our world."

But Rand's speech is also a step away from his father's ideals. After this speech, it's easy to imagine Ron and Rand debating each other on foreign policy. Rand says that we ought to bomb ISIS but not arm Syrian rebels. His father would reply that bombing ISIS would invite another 9/11 in response. When it comes to Iran and its nuclear ambitions, Rand says let's negotiate. Ron would say nuclear arms are Iran's business not ours, and let's investigate the CIA for its role in Iran in the 1970s.

Ultimately, the senior Paul did not have a foreign policy. Instead, he had a series of protests against the federal government. They were often richly deserved, but rarely did they constitute a genuine alternative to the status quo.

Rand could have gone in this direction. And he has shown that he's willing to take a protest to great lengths. Recall his popular filibuster against the use of drones in the United States, into which he folded criticisms of the Patriot Act and the presidential "kill list" that includes American citizens. But the younger Paul has decided that if he wants to be president, he better have a substantive foreign policy.

From both a political and policy perspective, it's interesting that Paul in his speech leaned into criticism of the intervention in Libya. It is a conflict that many people have forgotten about, and one that has resulted in little cost to the United States. Paul criticized the baleful result: a country plunged into even more violence and chaos, where its own government cannot even meet in the capital city. But Paul also went on to say that the war was illegal under the Constitution, as it received no authorization from Congress. Focusing on Libya may have a political purpose, too, as it was an intervention spearheaded by Hillary Clinton, and for which she took enormous credit when the results looked good.

Paul's step toward realism is also necessary considering the foreign policy dynamics within his own party. There are three intellectual camps in the Republican foreign policy tent: the neoconservatives, realists, and the various anti-interventionists. Since the end of the Cold War, realists have tended to defer to neoconservative and liberal hawks at the beginning of an intervention, then gravely furrow their brows later; think Condoleezza Rice, Chuck Hagel, or Jon Huntsman. By leading anti-interventionists toward realism, Paul is creating conditions within his own party, and within the world of policy expertise, for an American foreign policy that really does look different than the post-Cold War consensus.

Along the way, Paul's made some odd compromises. His speech was probably too hawkish on Russia, and too bullish on the power of sanctions. (What exactly did sanctions achieve in Cuba, Iraq, or in Moscow short of expressing hostility short of war?) But if Hillary Clinton does decide to run, Paul has probably found the sweet spot for advocating the foreign policy of restraint he believes in, while satisfying a partisan desire for contrast. This is good news for anyone interested in not repeating the disasters America has experienced in Iraq or Libya.