Why did Truman publicly announce the h-bomb project?
There are some perplexing aspects to Truman's announcement of January 31, 1950. First of all, whatever happened to secrecy? Besides, at the time of the announcement nobody had a clear idea of how to make the superbomb. Scientists figured it was probably possible, but the announcement predates the Teller/Ulam breakthrough. (It would have been embarassing if the announcement led to this being invented elsewhere first!)
The "natural" time to make such a public statement would have been after the Ivy Mike test, at the earliest.
Was it politics? Perhaps a political need to show toughness after the Soviet nuclear test?