Can the US still prevent an all-out Middle East war? 

And for Israel's No. 1 ally, the United States, the question is whether US President Joe Biden and his vice president, Democratic nominee Kamala Harris, can prevent such a politically hazardous escalation with little over a month to go in a very tight US presidential election.

On Tuesday, Harris's Republican opponent, former President Donald Trump, said the Iranian missile strike against Israel only exposed the lack of leadership from the Biden-Harris administration and pushed the world closer to a "global catastrophe."

There are many in Israel who, suddenly full of confidence a year into what has come to be seen as an existential fight against Iran and its proxies, now want a wider war against Tehran. "For Israel, Judgment Day has arrived," said Reuel Marc Gerecht, a former CIA officer now at the Foundation for Defense of Democracies (FDD). "The go-big argument has more currency in Israel now. October 7 and (Iranian Supreme Leader Ali) Khamenei's subsequent audacity have likely changed Israeli risk tolerance."

Many Israeli hawks, such as former Prime Minister Naftali Bennett, believe Iran's brazen willingness to fire ballistic missiles directly at Israel—not once but twice since a retaliatory attack in April—should be a trigger for a decisive response that eliminates any strategic threat from Tehran.

"Israel has now its greatest opportunity in 50 years to change the face of the Middle East," Bennett posted on X on 1 October. "We have the justification. We have the tools. Now that Hezbollah and Hamas are paralysed, Iran stands exposed."

"I think it's fair to say that if the Israelis don't go big after Iran's second invitation for them to do so, then they have accepted the Iranian bomb," said Gerecht, who also sees an attack on Iran's nuclear programme as a strategic imperative. Israel has a "perplexing question before it: If they strike Iran in any significant way (oil industry, military installations, senior leadership, including Khamenei) but don't go after the nuclear weapon infrastructure, then they could wound the theocracy but leave intact the one weapon that can deter further Israeli retaliation for Iranian machinations."

But such an escalation is the last kind of response that Biden and Harris want to see right now. As a proverbial "October surprise," it would entail a major regional war that would almost certainly suck in the US military and possibly cause American casualties, imperilling Harris's chances on 5 November. So the main diplomatic question is whether Biden can muster the leverage to prevent an escalating series of Israeli strikes either on Iran's leaders or its critical infrastructure facilities that would mean a full-blown war.

Indeed, it's very possible that Iran timed and calibrated its Tuesday attack knowing that Biden and Harris would work overtime to avoid a wider war. "I think the Iranians are banking on a Hail Mary" from the United States to prevent an all-out war, said Behnam Ben Taleblu, a senior fellow at FDD and an expert on Iran's missile capabilities.

Recent months do not supply much cause for hope that US diplomacy can make headway—especially since Biden became a lame duck with his 21 July announcement that he would not, after all, run for a second term at the age of 81. Even before then, Netanyahu was openly tweaking the US president, repeatedly ignoring US pleas for restraint and seeming to agree to a US cease-fire proposal for Gaza and then undercutting it.

Still, for most of the past year at least, Netanyahu appeared to be deferring to US pleas not to open a new front against Hezbollah and Lebanon. That all ended in September when, without even notifying Washington of its plans, Israel opened up that front with a high-tech sabotaging of Hezbollah pagers and walkie-talkies, killing at least 42 people and wounding thousands. It then assassinated Hezbollah leader Hassan Nasrallah and a senior IRGC commander, Abbas Nilforoushan, and followed up with a limited ground invasion, which is ongoing.

For Biden, the biggest problem is that "Washington is boxed into a corner," said Nimrod Novik, a former senior advisor to Israeli Prime Minister Shimon Peres. "Any demonstration of daylight between the US and Israel is bound to embolden all hostiles—Iran included. So Washington must stand by Israel even when it attacks, though thus far every American statement accentuated a commitment to defend Israel when attacked."

And whatever Israel does now, Ben Taleblu said, "I think it's gonna be massive." Though it avoided the sorts of Israeli casualties that would have certainly triggered an all-out Iran-Israel war, Tehran has crossed a red line by launching the "biggest ballistic missile barrage in history" against another country, Ben Taleblu added.

Analysts believe that on the whole, Tehran has sought to carefully calibrate its response to Israel's attacks, especially with a new, more moderate government led by President Masoud Pezeshkian seeking to reopen nuclear negotiations with the United States in return for lifting sanctions. Pezeshkian's vice president for strategic affairs, Mohammad Javad Zarif, was Iran's chief negotiator on the 2015 nuclear deal, known as the Joint Comprehensive Plan of Action.

Though Tuesday's missile attack involved more firepower—entirely composed of some 180 ballistic missiles fueled by higher-grade solid propellant—and giving fewer hours' notice than the April attack, it was also clear that Tehran sought to preserve the balance of its huge arsenal, said to be about 3,000 missiles. Iran also tried to make the case—as it did in April—that the cycle of escalation should now end.

"Essentially, Tehran is signalling to Israel that it would be fine with limited exchanges aimed at military targets," said Hussein Banai, a scholar at Indiana University and co-author of Republics of Myth: National Narratives and the US-Iran Conflict. "So if Israel hits back in a similar fashion, then I think Khamenei and co. will be happy to leave it there. But this is a critical decision point for (Netanyahu). If he chooses to go beyond the scale of the Iranian attack in retaliation to (Tuesday's) missile attacks from Tehran, then it could force Tehran's hand to abandon its strategy of controlled escalation."

Still, the Biden administration may have more leverage on this issue than it had against Israel's operations along its borders. A wider war with Tehran would require far more US military and intelligence cooperation. And many within Israel's national security apparatus are wary of overconfidence and hubris—especially knowing that the job against Hamas and Hezbollah is far from finished.

"These are experienced, thoughtful, and sober professionals," Novik said. "They know how powerful we are—but know the limits of our power. Also, unlike Netanyahu, they have nothing but respect for the US defence establishment, appreciation for the unprecedented help extended by the Biden administration, and take seriously the need to coordinate closely with Washington on matters affecting US national security."

On Wednesday, Biden told reporters that he wouldn't support an Israeli strike against Iran's nuclear facilities. He said the United States and its Western allies are mulling new sanctions against Iran, though US officials say they also expect some kind of Israeli military response.

"We will be discussing with the Israelis what they are going to do," Biden said, adding that he and the other G-7 leaders "agree that they have a right to respond, but they should respond in proportion. ... We are giving them advice. I will talk to Netanyahu relatively soon."

The coming days and weeks will tell whether that advice takes or a bigger war ensues.