The killing of Iranian Maj. Gen. Qasem Soleimani in a U.S. drone attack has exposed the limitations of the Trump administration’s “maximum pressure” campaign on Iran as it moves into a riskier, more confrontational phase.

Until recently, the pressure has been mostly economic — a stream of sanctions on more than 1,000 people, groups and companies associated with Iran that has crippled the country’s economy. The goal was to force Iran to negotiate a new nuclear agreement and act like a “normal nation,” as Secretary of State Mike Pompeo has said.

Neither is likely any time soon.

The sanctions have put the Iranian regime on the ropes economically, but they have not forced the Iranians to change their behavior or negotiate the deal. Instead, the campaign has pushed the fight further into the military realm, where Iran can exert its own form of maximum pressure on the United States.

The Trump administration and its defenders say the strategy has been working, and this is no time to change course.

The question now is which strategy will survive.

“The entire point is to box the regime in, to make them realize that they need to settle for a suboptimal solution, otherwise the pressure will only compound,” said Behnam Ben Taleblu, an Iran expert with the Foundation for Defense of Democracies.

“Prudent planning dictates that Washington also respond to Iran when needed, to keep it in the box. The strike against Soleimani, after six months of patience, is one such example.”

Washington and Tehran have been at loggerheads since the 1979 revolution and the siege of the U.S. Embassy in Tehran. But previous administrations have avoided direct confrontations and usually taken a more subtle approach. In his 2009 inauguration speech, for example, President Barack Obama promised to “extend a hand” if countries like Iran were willing to “unclench their fists.”

President Trump came to office determined to undo what he called the “terrible” 2015 nuclear deal the Obama administration negotiated with Iran and six other major powers.

The term “maximum pressure” became common foreign policy lingo when former secretary of state Rex Tillerson started using it to describe sanctions against North Korea. The administration also has applied it to the Maduro government in Venezuela. So far, it has not made any government surrender or significantly shift its positions.

But Iran has been the target of the most maximum-pressure tactics. In one of his first speeches after taking office in 2018, Pompeo threatened Iran with the “toughest sanctions in history” if it did not meet 12 demands, which included respecting human rights, withdrawing support for “terrorist groups” in neighboring countries and abandoning its missile development.

For a while, Iran continued to meet its commitments under the nuclear deal, even after Trump withdrew from the agreement in 2018. But its tactics changed after the United States began imposing more economic punishments.

The sanctions have been brutal on Iran’s economy, leading to mass protests around the country against fuel price increases. Iran’s leaders have instituted a harsh crackdown, killing at least hundreds of protesters and jailing thousands, human rights groups say. But the punishing sanctions have done did little to alter Iran’s actions or curb its destabilizing influence in the region.

Critics of maximum-pressure sanctions say the policy has backfired.

“Iran isn’t in a corner; we’re in a corner,” said Barbara Slavin, director of the Future of Iran Initiative at the Atlantic Council. “Trump has no good options. What more can the U.S. do now? We’ve sanctioned everything and everybody. What’s left?”

Iran has fought back against sanctions militarily, first by attacking oil tankers, shooting down a U.S. drone and striking oil facilities in Saudi Arabia, one of its main rivals. When the administration did not respond militarily, Iran became more aggressive.

“Iran started to ratchet up more conventional military actions to show it could not be pushed around,” said John Glaser, the Cato Institute’s director of Foreign Policy Studies.

Glaser said the maximum-pressure campaign has worsened the already adversarial relationship between Washington and Tehran.

“Trump came into office with Iran denuclearized and with an open channel of communication in place for the first time in 40 years,” he said. “Now there’s no diplomatic channel. They’ve been imposing sanctions without signaling what Iran could do to get them lifted. Pompeo’s demands were a way of saying they will never get lifted, unless they get rid of their entire foreign policy and reform their entire system. Iran saw itself with little option.”

Since early October, the administration has counted 10 attacks in the Baghdad area alone from militias allied with Iran. A turning point came on Dec. 27, when an American contractor was killed in a rocket attack in northern Iraq. The administration had signaled for months that it would hold Tehran responsible for the acts of militias and responded two days later with airstrikes against five of the group’s facilities Iraq and Syria.

The conflict escalated when pro-Iran protesters stormed the U.S. Embassy in Baghdad on New Year’s Eve, prompting the strike that killed Soleimani, the commander of Iran’s elite Quds Force.

U.S. officials show no signs of backing down from the strategy of maximum pressure and view it as a success. They say the economic devastation has put Iran’s ruling clerics on their heels, ensnaring them in the worst economic and political crisis in their four decades of power as Iranians grow more fed up with the diversion of money to foreign adventures.

“Maximum pressure has been a successful strategy,” said Fred Fleitz, who worked in the White House as chief of staff to former national security adviser John Bolton and now is president of the Center for Security Policy.

“It’s put enormous pressure on the Iranian economy. The protests and attacks shows the regime’s desperation. The president is giving Iran a choice. It can start negotiating, or maximum pressure will continue.”

But Slavin said the Iranian government crackdown has left the opposition leaderless and turned Soleimani into a martyr.

Iran’s leaders are “probably going to play it for everything it’s worth,” she said. “This regime will survive Donald Trump.”