The following is the June 21, 2018 Congressional Research Service Report, The Purple Heart: Background and Issues for Congress.
From the Report:
The Purple Heart is one of the oldest and most recognized American military medals, awarded to servicemembers who were killed or wounded by enemy action. The conflicts of the last decade have greatly increased the number of Purple Hearts awarded to servicemembers.
Events over the past few years have spurred debate on the eligibility criteria for the Purple Heart. Shootings on U.S. soil and medical conditions such as traumatic brain injury (TBI) and posttraumatic stress disorder (PTSD) have prompted changes to the eligibility requirements for the Purple Heart. Some critics believe that these changes may lessen the value of the medal and the sacrifices of past recipients on the battlefield. In the past, efforts to modify the Purple Heart’s eligibility requirements were contentious, and veterans groups were very vocal concerning eligibility changes.
While medal requirements are often left to the military and executive branch to decide, Congress is showing increased interest and involvement in Purple Heart eligibility, utilizing its constitutional power “To Make Rules for the Government and Regulation of the land and naval Forces” (U.S. Constitution, Article I, Section 8, clause 14). The Carl Levin and Howard P. “Buck” McKeon National Defense Authorization Act for Fiscal Year 2015 (P.L. 113-291) included language that expands eligibility for the Purple Heart.
Previous debates have raised several questions about the Purple Heart. In some respects, how an event is defined can determine eligibility: Is a servicemember the victim of a crime or a terrorist attack? Conversely, arguing that killed or wounded servicemembers “should” be eligible for the Purple Heart can redefine an event: Is the servicemember an advisor to a foreign military or a combatant? Are PTSD and other mental health conditions adequate injuries to warrant the Purple Heart? These are questions that Congress might consider if it chooses to act on this issue.