The New York Times, citing officials from the Trump administration:

Trump, at least for now, has stepped back from his plans for a broad escalation of U.S. military attacks against Iran. One of the main concerns is that expanding the war could further deplete the Pentagon’s dwindling stockpiles of Patriot interceptor missiles and other air-defense munitions in the Middle East.

Threats to interceptor-missile stockpiles are one of the key factors that have made a return to large-scale military operations a high-risk move.