That can't be answered properly without knowing from proper investigation all the individual circumstances of all four accidents.
Presumably all the air transport safety laws and practices are still as normal.
It may be that nothing is "going on" beyond a terrible co-incidence; but no-one, particularly the bereaved, is served by those trying to use the accidents for party-politics before the investigators have determined the cause of each crash.
Only then can the US Government determine if there have been any deleterious political, economic or legal influences on flying safety, and the appropriate actions if so.