Less than two hours after President Trump announced on social media that he had ordered military strikes on Iran, Representative Alexandria Ocasio-Cortez, the ultraprogressive Democrat from New York, denounced the move as “disastrous,” a “grave” violation of the Constitution and grounds for his impeachment and removal.

The Democratic leaders in Congress, Senator Chuck Schumer and Representative Hakeem Jeffries, both of New York, were more muted in their statements. They castigated the president for not consulting Congress and warned that his action had “dramatically increased” the chances of a broader war in the region, but they didn’t condemn it outright.

The contrast reflected deep divisions among Democrats over how to respond to Mr. Trump’s decision, the latest dispute inside the party about the best way to counter a president who holds a lock on Congress and is eager to push the boundaries of his power.

The debate has resurfaced longstanding fault lines in the party over the use of military force and the role of Congress in exercising it, with antiwar liberals urging restraint and more hawkish centrists backing more aggressive action. But this time it is also fueled by a newer and more bitter political rift in Democratic ranks over support for Israel, which has become one of the most polarizing issues for the party.

Progressives like Ms. Ocasio-Cortez who have been outspoken about criticizing Israel and American support for the nation were among the first and most vocal in condemning Mr. Trump’s decision to back Israel’s war against Iran by striking its nuclear facilities. But party leaders and many pro-Israel Democrats in the rank and file, even as they were fiercely critical of Mr. Trump, worded their statements carefully, wary of saying or doing anything that could be construed as hostile to Israel.