Updated June 20, 2019

WASHINGTON — Iran’s shooting down of an American surveillance drone on Thursday and the attacks on two tankers in the Gulf of Oman last week have again sent the United States and Iran, two longtime adversaries, hurtling toward potential crisis. The challenges are diplomatic and economic as well as military.

But that course was set a year ago, foreign policy experts say, when President Trump, enforcing his “maximum pressure” campaign against Tehran, withdrew the United States from an Obama-era agreement meant to rein in Iran’s nuclear ambitions.

“Iran was getting repeatedly punched in the face by the Trump administration, and they’ve been warning for months there will be consequences,” said Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace. “The Iranian economy has long been riddled by endemic mismanagement, corruption, cronyism, and brain drain. Sanctions makes all these problems worse.”

Here’s a look at how the United States turned up the pressure on Iran.