On June 21, President Trump came within minutes of starting an all-out war with Tehran by launching airstrikes against Iranian targets in response to the downing of a U.S. drone. But with planes in the air and missiles primed, Trump canceled the order, stunning his closest political advisers.

Almost exactly six months later, Trump had no second thoughts, green-lighting the assassination of top Iranian General Qassem Soleimani in the early hours of Friday morning as he left Baghdad International Airport with a number of top Iraqi militia leaders.

The attack has sparked outrage in Tehran, with tens of thousands of Iranians taking to the streets chanting “Death to America!” and Iran’s top leaders promising “forceful revenge” against the U.S. for what they call “a heinous crime.”

The Islamic Revolutionary Guard Corps said it is awaiting orders, and Iran’s fighter jets were scrambled, but even though Iran can’t confront the U.S. military directly, Iran has options. Among them: strikes against the numerous U.S. military targets in the region, stepping up its support of proxy forces fighting the U.S.and its allies across the Middle East, and perhaps most ominously, cyberattacks on vulnerable U.S. cities and infrastructure.

“I would expect some combination of cyber, proxy and terrorist attacks on U.S. interests in the Middle East but also outside the region, in Europe and/or the U.S. homeland,” Michael Carpenter, who served on the national security council during the Obama administration, told VICE News.

All-out war

Iran has been suffering under crippling economic sanctions imposed by the U.S. since it withdrew from the nuclear arms deal in May 2018, so it will have little appetite for a costly war with a powerful and well-resourced U.S. military.

Trump, too, has long declared that he does not want a war with Iran and promised to pull all U.S. troops out of the region. But the actions taken by his administration over the last two years tell a different story.

“Trump keeps on saying he doesn't want [a war], yet he keeps on doing things that escalate matters, starting off with walking out of the nuclear deal and essentially conducting economic warfare against Iran,” Trita Parsi, executive vice president of the Quincy Institute, a Washington-based think tank, told VICE News.

While basic geography means Iran cannot mount a direct attack on U.S. soil, there are more than enough U.S. targets dotted around the Middle East for it to attack if its leaders wanted to, including U.S. military bases or a U.S. warship stationed in the Persian Gulf.

The most obvious point of such an attack would be Iraq, Iran’s closest neighbor, where over 5,000 U.S. troops are stationed.

’Iran's response will likely be a combination of direct and indirect responses aimed at targeting U.S. military infrastructure and even personnel’

“Iran's response will likely be a combination of direct and indirect responses aimed at targeting U.S. military infrastructure and even personnel,” Sanam Vakil, a senior research fellow at London-based think tanks Chatham House, told VICE News. “Iraq is the most likely area where Iran can and will strike first, but the U.S. should not rule out strikes in the Persian Gulf.”

Such an attack would likely trigger a swift and deadly response from Washington, something Tehran will be keen to avoid, and so Iran may rely instead on a tactic where it can compete on a relatively level playing field.

Cyber warfare

Pentagon officials speaking to U.S. media have already said they are especially concerned with Tehran launching cyberattacks against targets on U.S. soil — and with good reason.

In the recent past, Tehran’s state-backed hackers have targeted banks, casinos, the city of Atlanta, and a dam just outside New York as part of its campaign of cyberattacks against U.S. targets.

While Iran cannot compete with the U.S. military when it comes to tanks or warships, it has grown increasingly sophisticated in cyberspace in recent years.

“They are still behind in capability to other top-tier states such as the U.S., Russia, and China but can sometimes be more aggressive and willing to be destructive; therefore, they're still a serious threat,” Robert Lee, CEO of Dragos, a cybersecurity firm that specializes in protecting industrial control systems, told VICE News.

Chris Krebs, the director of the Cybersecurity and Infrastructure Security Agency, highlighted a warning he issued last June about heightened Iranian activity on U.S. networks.

“Iranian regime actors and proxies are increasingly using destructive ‘wiper’ attacks, looking to do much more than just steal data and money,” Krebs said at the time. ”These efforts are often enabled through common tactics like spear-phishing, password spraying, and credential stuffing. What might start as an account compromise, where you think you might just lose data, can quickly become a situation where you’ve lost your whole network.”

While defenses of U.S. networks have improved in recent years, there are many soft targets remaining, and as more and more of America’s critical national infrastructure gets connected to the internet, the bigger target it presents.

“When we look at industrial infrastructure — electric, water, natural gas, manufacturing, oil — there are some who have world-leading [security] programs but some who have done very little,” Lee said. “The good news is our infrastructure is highly reliable, and a culture of safety has added a sort of base level of security to people. But much more is needed to feel comfortable in scenarios like this.”

A proxy war

Soleimani spent decades forging close relationships among militia groups in countries across the Middle East, expanding Iran’s reach much further than its borders.

Experts have feared that these proxy forces will play a key role in any further escalation of tensions between the U.S. and Iran. One Iran-backed Iraqi militia commander has already ordered his men to be ready for an upcoming battle.

One of Souleimani’s most successful proxy projects was the formation of Hezbollah, a Shiite paramilitary group and political party in Lebanon. Iran supplied the group with weapons during its conflict with Israel in 2006 and more recently has supported its intervention in the bloody nine-year Syrian civil war.

The proxy war between the U.S. and its allies and Iran and its allies has already begun, as we’ve seen with U.S. economic sanctions and Iran’s attacks on oil tankers and Saudi oil facilities. But Soulemani’s assassination could ignite this simmering conflict.

"It is very difficult to say that this is just going to remain between the U.S. and Iran because it's already outside of the U.S. and Iran: It's taking place in Iraq, it's taking place in the Persian Gulf, it's taking place, apparently, in Saudi Arabia and Yemen,” Parsi said. “The question now is, will it go beyond that?”