Consider three types of case. (a) A Muslim terrorist who was born in the USA and whose terrorism derives from his Islamic faith. (b) A Muslim terrorist who was not born in the USA but is a citizen of the USA or legally resides in the USA and whose terrorism derives from his Islamic faith. (c) A terrorist such as Timothy McVeigh who was born in the USA but whose terrorism does not derive from Islamic doctrine.
As a foe of obfuscatory terminology, I object to booking the (a) and (b) cases under the 'homegrown terrorist' rubric. In the (a)-case, the terrorist doctrine, which inspires the terrorist deeds, is of foreign origin. There is nothing 'homegrown' about it. Compare the foreign terrorist doctrine to a terrorist doctrine that takes its inspiration, rightly or wrongly, from American sources such as certain quotations from Thomas Jefferson or from the life and views of the abolitionist John Brown.
The same holds a fortiori for the (b)-cases. Here neither the doctrine nor the perpetrator are 'homegrown.'
There is no justification for referring to an act of Islamic terrorism that occurs in the homeland as an act of 'homegrown' terrorism.
The (c)-type cases are the only ones that legitimately fall under the 'homegrown terrorist' rubric.
So please don't refer to Ahmad Khan Rahami as a 'homegrown terrorist.' He is a (b)-type terrorist. There is nothing 'homegrown' about the Islamic doctrine that drove his evil deeds, nor is there anything 'homegrown' about the 'gentleman' himself. Call him what he is: a Muslim terrorist whose terrorism is fueled by Islamic doctrine.
The obfuscatory appellation is in use, of course, because it is politically correct.
Language matters. And political correctness be damned.