From the Document: "Since May 2019, U.S.-Iran tensions have escalated. The Trump Administration, following its 2018 withdrawal from the 2015 multilateral nuclear agreement with Iran (Joint Comprehensive Plan of Action, JCPOA), has taken several steps in its campaign of applying 'maximum pressure' on Iran. Iran and Iran-linked forces have targeted commercial ships and infrastructure in U.S. partner countries. U.S. officials have stated that Iran-linked threats to U.S. forces and interests, and attacks on several commercial ships in May and June 2019, have prompted the Administration to send additional military assets to the region to deter future Iranian actions. However, Iran's downing of a U.S. unmanned aerial aircraft might indicate that Iran has not been deterred, to date."
CRS Report for Congress, R45795
Congressional Research Service: https://crsreports.congress.gov/