US President Donald Trump has summed up his rationale for attacking Iran fairly simply, saying “this was our last best chance to strike”. Not known for adhering to any particular lasting strategy, Trump sees each day in the White House as an episode in a reality show in which he seeks an advantage over his rivals, if not to vanquish them. And Iran certainly qualifies as one of America’s most enduring rivals.To be sure, Trump’s claim that Iran posed an imminent threat to the US is hard to justify. After all, Iran’s military and proxy groups have never been weaker. It’s also hard for him to claim that Venezuela or Islamic State operatives in Nigeria, Syria and Iraq posed imminent threats to the US. Nonetheless, the Trump administration struck all of them over the past year.As much as Trump may have campaigned against nation-building and “forever wars” when running for president, he certainly never campaigned against military strikes, particularly ones that entail minimal danger to American lives.Trump campaigned in 2016 on strengthening the US fight against Islamic State. And once in office, his administration not only helped eliminate the IS caliphate – finishing the job started under the Obama administration – but also killed IS leader Abu Bakr al-Baghdadi. The first Trump administration was also behind the assassination of Iranian commander Qassem Soleimani in a brazen attack near Baghdad airport.It is likely for this reason his administration decided to go for the death blow now, when the Iranian government is at its most vulnerable.There were also specific circumstances that have made Trump more open to limited military actions in the past: long-lasting, bipartisan frustration with an adversary the support of regional US allies and partners for a strike (or at least their toleration) US capability to mitigate potential responses. And there was another undeniable factor: the increasing confidence that comes from the perceived success of previous actions. Many expected the Trump administration’s capture of Venezuelan President Nicolas Maduro to result in chaos, for instance, but that has yet to happen. Trump in 2019: ‘Great nations do not fight endless wars.’ Decades of antagonismThis is undoubtedly a war of choice, not necessity. That said, the Trump administration is likely hoping the US can be less involved in the Middle East after this war, if it results in a different Iran. The sentiment that fuels Trump’s antagonism towards NATO allies is the same that is motivating his war against Iran: the US wants to do less overseas. Such a statement may appear ironic given the administration has undertaken America’s largest military attack since the invasion of Iraq 23 years ago. But this is presumably the administration’s end game with Iran, risky as it may be.Half a century ago, Iran was second only to Israel among Middle Eastern countries with close working relationships with the United States. The post-1979 Islamic Republic, however, upended the region’s power dynamics. Iran’s top foreign policy priorities for decades have been projecting hostility towards the United States and Israel.In that time, Democratic and Republican administrations alike have labelled Iran the world’s foremost state sponsor of terrorism. For years, Iran has proudly supported Hamas in Gaza, Hezbollah in Lebanon, the Houthi rebels in Yemen, Bashar al-Assad’s regime in Syria, and Shia militant groups in Iraq. Such groups have killed hundreds of Americans and tens of thousands of others across the Middle East. Iranian agents also sought to assassinate Trump and other senior US officials. Iran and its proxy groups have cost successive American administrations – both Democratic and Republican – enormous political capital and resources for decades. It should also be said the vast majority of Iranians are against the regime and have never felt more optimistic about a brighter future since the Islamic Revolution in 1979. Limiting factors moving forwardUS Defence Secretary Pete Hegseth has tried to distinguish the Iran war from the “forever wars” of the past, saying, “This is not Iraq, this is not endless”. The administration is likely aware of other key differences, too. Compared to George W. Bush’s war against Iraq in 2003, Trump has lacklustre support for the Iran strikes. Democratic lawmakers have called the attack both unconstitutional and against international law. Only 55% of Republicans support the attack, despite the fact Trump himself enjoys an approval rating among members of his party of around 80%. The Trump administration hasn’t helped itself with its incoherent messaging, either. It has used a number of justifications for the strikes, including stopping an imminent Iranian attack, destroying Iran’s ballistic missiles, preventing it from acquiring nuclear weapons, cutting off support for its proxy militant groups, and regime change. Most recently, the administration said it had to join Israel’s offensive against Iran because it was going to be drawn in by Iran’s response anyway. And Trump refused to rule out boots on the ground in Iran. These conflicting messages don’t help sell the operation to a wary public, particularly one that is far more concerned about the economy than the Middle East. After all, the last time a foreign policy issue played a significant factor in a US election was arguably more than 20 years ago.So, why engage in such an expensive and risky endeavour that even his own base doesn’t fully support? One reason is the US constitution allows the president to do a lot more to change the dynamics on the ground in Iran than it does in the United States. The judicial branch, for instance, has limited Trump’s “Liberation Day” tariffs and deployment of federal troops domestically. Foreign policy is one area where he can be a man of decisive action. But Trump knows a long war is not feasible. The US, Israel and their regional allies and partners face the real prospect of running low on munitions to continue defending against Iran’s far cheaper drones for the weeks or months that Trump says the war may continue. The Islamic Republic of Iran is also facing an existential battle for its survival. The regime’s will to fight and ruthlessly effective internal security forces – combined with low US domestic support for war – means time may be on its side. Facing increasing levels of domestic opposition, we can expect the Trump administration to try to avoid a long-term conflict in Iran. As history shows, however, it still needs an exit strategy.Jared Mondschein does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.