When Rand Paul speaks on college campuses, he has a simple message: "I'm not here to send you to war."

Slumping in the polls and struggling to raise money, that's increasingly the raison d'etre of Paul's presidential campaign. In media interviews, he rails against a U.S.-enforced no-fly zone over Syria that has been proposed by both Hillary Clinton and Republican candidates like Chris Christie, arguing that it would repeat the blunder of Iraq and even risk a World War III involving a nuclear-armed Russia.

"I think it's the world's dumbest idea and a recipe for disaster, a recipe for war," Paul told the conservative Washington Times. And that's why, in spite of everything, he's still running.

"If I'm not in the race," Paul added, "that voice doesn't get heard. A lot of Americans are with me and think we need a more prudent foreign policy."

Not Clinton, however. In the first Democratic debate, she doubled down on her defense of the U.S.'s intervention in Libya. That fiasco gave rise to the Benghazi consulate attack that has been whipping Republicans into a frenzy for three years, and her nonchalance demonstrates that she has learned nothing from her vote for the Iraq War.

One of the reasons Paul has struggled this year is that hawkish Republicans have successfully branded President Obama as a virtual noninterventionist on foreign policy. From ISIS in Iraq to Russian intervention in the civil war in Syria, the narrative is that Obama's retrenchment and retreat have created a vacuum that has been filled by the world's bad actors.

That Obama has launched two wars without the constitutionally required approval of Congress, proposed a third, extended a fourth in Afghanistan, and helped exacerbate a fifth in Yemen, all while conducting controversial drone strikes, tells a different story, but one that largely goes untold.

The biggest foreign policy risk for Paul in the 2016 campaign has never been that the establishment wrongly thinks he's an isolationist. It is the possibility that the Republican base will think he either supports or does not differ sharply enough from Obama's foreign policy.

On Libya, Syria (in 2013), drone strikes, and surveillance, the anti-interventionist position was also the anti-Obama position. On Cuba and Iran, to name just two examples of foreign policy issues that have come up since Paul declared his candidacy for president, the hawks can most easily position themselves as anti-Obama.

But Clinton is a liberal hawk to a much greater extent than Obama. In debating the more interventionist members of his own party, Paul must ask why these otherwise conservative Republicans agree with Clinton on so many foreign policy issues, including "Hillary's war" in Libya.

For one thing, last week's debate makes clear that none of the Democrats are up to the challenge. Jim Webb was prescient on the Iraq War, but seemed more interested in quibbling with Anderson Cooper about his speaking time — he has now dropped out of the race for the Democratic nomination. The well-meaning but unimpressive Lincoln Chafee said he is running against Clinton because of her Iraq War vote, while in the same breath made lame excuses for his own votes that he's come to regret. Bernie Sanders has opposed wars Clinton has supported, including in Iraq. But he'd rather not talk about foreign policy or criticize Clinton overmuch. And Sanders has arguably been more hawkish than Webb or Chafee.

Republican hawks never hesitate to point out when conservatives like Paul agree with liberals like Dennis Kucinich on a foreign policy issue. Why not do the same when these Republicans side with Obama and Clinton on arming "moderate" Syrian rebels to little obvious benefit, or when they vote with Clinton, Joe Biden, Harry Reid, and John Kerry to invade Iraq?

Ted Cruz seems to get it. "Look, we have no business sticking our nose in [Syria's] civil war," he told NBC's Chuck Todd. "And there are a lot of politicians, including Hillary Clinton on the left and including quite a few of the Republicans running for president on the right, who want us to get in the middle of that civil war."

But Cruz is an inconsistent intervention skeptic at best.

Donald Trump, after Paul the least hawkish Republican candidate, has been running against George W. Bush, sometimes drawing in liberal Democrats himself. Paul seems tempted to run against Trump. This is a mistake.

Even in this age of "pox on both houses" independents, politics remains for most Americans a partisan affair. The best way to convince conservatives that they should be as skeptical about wars as other large-scale government undertakings is to point out how liberal Democrats like Clinton have often been almost as eager to take the country to war as to give it government health care.

The last, best chance for Paul to have an impact on the Republican race is to start running against the relatively hawkish Democrat who is likely to become her party's nominee.