ICBMs didn't exist at the time -- intercontinental capability didn't arrive until the Soviet R-7 missile in 1957, eight years after the first successful Russian nuclear test, and no missiles were tested with nuclear warheads until 1958 -- making the strategic picture dependent at least as much on air superiority as on the state of nuclear tech. Between geography and military focus, that would probably have given the United States a significant advantage if they'd chosen to pursue this avenue in the mid-to-late 1940s. On the other hand, intelligence services were pretty crude in some ways, too; my understanding is that the Russian atomic program was unknown to the American spook establishment until it was nearing completion.