"Successive Administrations have identified Iran as a key national security challenge, citing Iran's nuclear and missile programs as well as its long-standing attempts to counter many U.S. objectives in the region. The Trump Administration has defined Iran and its regime as a particularly significant threat to U.S. national security, accusing the regime of 'destructive behavior at home and abroad.' Director of National Intelligence Dan Coats, in his February 13, 2018, annual worldwide threat assessment testimony before Congress, assessed that 'Iran will seek to expand its influence in Iraq, Syria, and Yemen, where it sees conflicts generally trending in Tehran's favor' and 'Iran will develop military capabilities that threaten U.S. forces and allies in the region.' Successive National Defense Authorization Acts (NDAAs) have required an annual report on Iran's military power, which has in recent years contained assessments of Iran similar to those presented publicly by the intelligence community."
CRS Report for Congress, R44017
Congressional Research Service: https://crsreports.congress.gov/