On June 21, President Donald Trump informed the world (via tweet) that after getting US forces "cocked and loaded" to carry out strikes on Iranian targets the night before, he had canceled those strikes at the last minute rather than prospectively kill 150 people. "Not proportionate," he wrote, "to [Iranian forces] shooting down an unmanned drone" earlier that week.
Anti-interventionists (including me) cheered the move. US hawks moaned that Trump had suddenly and inexplicably gone soft by avoiding the war they want so badly. Pretty much everyone thinks the "proportionality" claim isn't the true explanation, given Trump's over the top predisposition on most things.
But hey, I'll take it, and I'll thank Trump for it. Every time he avoids escalation toward outright war with the Iranians or anyone else, he's doing the right thing and should get credit for it.
As to the bigger picture, the question now is whether Trump will undo his earlier errors on US policy toward Iran instead of compounding them.
He doesn't seem inclined to. On June 24, he signed an executive order imposing new sanctions on Iran's Supreme Leader, Ayatollah Ali Khameini, and Foreign Minister Javad Zarif, also in retaliation for the downing of a US drone — possibly over Iranian airspace, certainly more than 5,000 miles from airspace it had any business in.
Unfortunately, Trump considers his warlike attitude toward Iran a campaign promise and seems to have every intention of keeping that promise. He was elected president on, among other things, his stated intention of undoing former President Barack Obama's most significant foreign policy accomplishment, the Joint Comprehensive Plan of Action, (the "Iran nuclear deal").
That JCPOA began winding down four decades of mutual belligerence that began when Iranians had the gall and temerity to overthrow a dictator installed by the US , replacing him with a government more to their own liking. In exchange for partial lifting of sanctions and return of some money stolen by the US government after their revolution, the Iranians gave up a nuclear weapons program they don't appear to have actually had, going above and beyond their already existing (and apparently kept) obligations under the Non-Proliferation Treaty.
Trump violated the deal, pretending that he was "withdrawing" the US from it (the deal is codified as a UN Security resolution; the only way to withdraw from it is to withdraw from the UN itself). He's reimposed US sanctions and pressured US allies to do likewise.