Anyway, if an interstellar civilization wanted to make contact with Earth, USA couldn't stop them. And in the highly improbable case that USA found a way to prevent their population from knowing, it's only one country, they'd have to convince every other country in the world to do the same.

Let's talk about congressmen insider trading instead.

If all major governments keep it secret, the conclusion would be that the phenomenon wants it that way. The US wouldn't be in charge. But apparently something changed.