Context: The President it was addressed to had been working to prepare for war against Germany for most of a year. Einstein's "famous, politically ~neutral super-genius" reputation was far loftier than that of any signatory to this Open Letter. And it warned the U.S. President about a super-powerful type of bomb which Germany might develop (and use against the U.S.A.) during a period when both bomber and bombing technologies were obviously advancing very rapidly.

If a "smartest in the world" mathematician wrote the current U.S. President, to warn that the crypto algorithms currently used by the U.S. for uber-secret stuff might quite possibly be fully broken by China in the next few years - then I suspect that the current U.S. President might be fairly willing to take action. That is not the scenario around this Open Letter.