When he walked into the President's office, he held enough power at that moment that he could have told Truman to get out of his (Oppie's) chair, and GTFO of his (Oppie's) office.

Obviously, in reality, it would have required much more planning and preparation, but that's essentially a statement of the balance of power at that moment in history.

The Soviets were clawing at the door to get this new superweapon (https://en.wikipedia.org/wiki/Atomic_spies), and even the UK - which was a partner in the bomb's development - was locked out of the technology (https://www.goodreads.com/book/show/28866320-test-of-greatne...).