WASHINGTON (AP) — President Donald Trump's explosive Twitter threat to Iran's leader comes as his administration is ratcheting up a pressure campaign on the Islamic republic that many suspect is aimed at regime change.

No one is predicting imminent war. But Trump's bellicose, all-caps challenge addressed to President Hassan Rouhani followed a speech by Secretary of State Mike Pompeo in which he accused Iran's leadership of massive corruption and widespread rights abuses and urged Iranians to rise up in protest.

Both the tweet and the speech landed less than two weeks before the administration...