Aeronautical expert I know reckons Concorde could have done the job more safely and cheaper. Only M2 and 60,000' but still high and fast enough to be untouchable.
But no need for special airfields or exotic fuels (it could operate just about anywhere). And perhaps most importantly, highly unlikely to suffer in-service losses due technical failures (lots of SR71s lost, none through enemy action).
Of course it came later than the SR71, but could have replaced it in service.