Republican foreign-policy circles have hailed Mitt Romney’s choice of Wisconsin Congressman Paul Ryan as his running-mate, noting that he believes in free trade, a strong defense, and is thinking seriously about China. Moreover, unlike the current resident of the White House, Ryan is an unabashed advocate of American exceptionalism. “A world without U.S. leadership will be a more chaotic place,” Ryan said in a speech delivered to the Alexander Hamilton Society last June. “A place where we have less influence, and a place where our citizens face more dangers and fewer opportunities. Take a moment and imagine a world led by China and Russia.”But let’s ask a practical question: How does Ryan’s selection affect Romney’s calculation in what is if not the most important foreign-policy issue for an American president, certainly the most pressing—the decision to use military force against Iran’s nuclear weapons facilities?The answer: It doesn’t.During Romney’s trip to Israel last month, campaign adviser Dan Senor said: “If Israel has to take action on its own, in order to stop Iran from developing that capability, the governor would respect that decision.” But that’s an important hedge, and it throws into sharp relief the real truth: A Republican president is no more likely than a Democrat to stage a pre-emptive attack on Iran, and American support for an Israeli attack is the very best that Israeli leaders can hope to expect from the White House, regardless of which party inhabits it.The explanation is based on three interrelated factors: domestic American politics, Washington’s history with the Islamic Republic of Iran, and the U.S. record of containing and deterring nuclear powers.Domestic politics. Bush did not attack Iran because he was already waging war in two Middle Eastern theaters and did not want to go down in the history books as the president who only waged wars on Muslims. Barack Obama has not attacked Iran in his first term and is highly unlikely to do so in his second term because his Middle East policy is one of extrication from the region, not further military involvement. Correctly or not, the Obama White House suspects that an attack on Iran will not only eventually entail landing ground troops but will also further inflame the Muslim world against America, and Obama is the president of outreach to the Muslim world.Romney’s internal conversation with himself will look something like a combination of his two predecessors’: He doesn’t want to further burden the economy by destabilizing the Middle East and sending oil prices skyrocketing, and he doesn’t want to be tagged as a war-mongering Republican who bombed Iran only a few months after moving into his new digs. Like every other man who takes the job, Romney wants a second term, and if he gets it, then there’s going to be another reason not to do it.History’s lessons. The record shows that there is always a reason for American presidents of both parties to look the other way when Iran is up to no good. No American president has ever drawn red lines for Tehran and enforced them by showing that transgressions are swiftly and severely punished.It’s true that it was a Democrat, Jimmy Carter, who sat by idly when Ayatollah Khomeini and the founders of the Islamic Republic stormed the U.S. embassy and held Americans hostage for 444 days. But GOP hero Ronald Reagan provided the Iranians with arms—after the Islamic Republic’s Lebanese asset, Hezbollah, killed 241 U.S. Marines in the 1983 bombing of their barracks at the Beirut airport. When the FBI said Tehran was responsible for the 1996 bombing of Khobar Towers, Bill Clinton failed to respond or even name Iran, lest it derail the “dialogue of civilizations” promised by the newly elected reform-minded president Muhammad Khatami. And the last Republican in the White House was no more proactive in countering Iran’s actual attacks on Americans: The more than 100,000 American servicemen and -women that Bush had dispatched to Iraq were targeted by the IRGC and their local allies, a fact that U.S. officials tended to obscure and did little to change when they did acknowledge it.The current administration, unsurprisingly, hardly broke this mold. After the Obama White House revealed the Islamic Revolutionary Guard Corps plot against the Saudi ambassador in Washington, it exacted no price from Iran for planning an operation in the American capital that might have cost the lives of hundreds of American citizens.General nuclear deterrence. If you can kill Americans without any consequences and the Americans will in fact collaborate in covering up your malfeasance, you can certainly build a nuclear weapons facility without too much concern that the Americans are really keeping “all options on the table”; the White House is not and almost surely never will—no matter who’s calling the shots. Short of an American city suffering thousands of casualties in a nuclear attack that the Iranians boast of publicly, it is difficult to know what would compel a U.S. president to take military action against Iran.Maybe U.S. policymakers just believe, in spite of what they say publicly, that Iran really isn’t that big a deal. Remember that even today, a number of American officials, civilian and military, cut their teeth on Cold War strategy, an era when the United States faced off against a real superpower. Washington and Moscow fought proxy wars against each other on four continents with the fear of an eventual nuclear exchange leading to mutually assured destruction looming in the background. Perhaps, if seen in this context, for American policymakers Iran just doesn’t rise to a genuine threat level.The Obama Administration says its policy is not to deter and contain an Iranian nuclear weapons program but to prevent it. But that’s just what they’re saying. What they believe surely must be something else. If the United States was able to contain and deter the Soviets, we can certainly do the same with a crummy little third-world regime like Iran’s. Or perhaps American policymakers just see it like this: If we take military action against Iran, the likeliest scenario is a region-wide war and an Iranian terror campaign against the United States and its allies, especially Israel. If we do nothing, the worst-case scenario is that emboldened Iranian action leads to a region-wide war and global terror. Common sense tells you that if someone believes he will get the same results by doing nothing and doing something, then he will choose the path of least resistance, by doing nothing.Surely by now Israeli leaders know that, given the various trend-lines of American policy toward Iran, no U.S. president is going to take military action against Iran. The most Israeli leaders can expect is for the White House to provide them with certain weapons and military hardware that might make the operation easier, and in the aftermath to provide plenty of diplomatic support.Earlier this week, Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey said of the Israelis: “They are living with an existential concern that we are not living with.” That’s an honest assessment, and so an honest conversation between allies could perhaps go like this: “It’s just not that big a deal to us, but if you guys feel you need to act, then go ahead. We’ll stand with you.” That seems to be what Senor was signaling when he said Romney as president would “respect” Israel’s decision.If Israeli leaders really thought Romney was much more likely than Obama to bomb Iran, there wouldn’t be so much chatter now right now about how it’s become crunch time for Israel. Bibi Netanyahu would at least give Romney the benefit of a few months after the November elections. But the Israeli half of the conversation is no longer about pressuring their American allies. Rather, it seems to be preparing the Israeli public for an attack.***Like this article? Sign up for our Daily Digest to get Tablet Magazine’s new content in your inbox each morning.Lee Smith is the author of The Consequences of Syria.