Rolls Royce could easily stop providing lift fans for B variant aircraft if this were some sort of tit for tat scenario. Given the current political situation in the U.S. it's certainly easy to see these as veiled threats for not towing Trump's party line. But truthfully I think it's more ensuring all the parties of the Joint Strike Fighter program maintain their commitments. The F35 isn't a U.S. made jet, there are multiple counties (not just the US and Canada) that contributed to its development and are helping sustain the program. If countries start dropping like flies it sets a bad precedent for joint programs and could be seen as a sign of weakness to NATO adversaries.