Good answers everyone.
The point of this topic isn't much to see the US joining the Central Powers, it's much to see an entente US, that discovers that was deceived to join a war.
About the USW, it's much better to rephrase it into some select RN subs attacking US shipping and using KM flags, uniforms and colors to fake a german attack.
But conspiracies are hard to do, but they are interesting to think. Zimmermann telegram have everything to be a conspiracy or ASB, because how idiotic it was, but the german government kinda liked it on time, reading from comments.
The US could discover it from spies, because they aren't 100% convinced on this, and is leaked to public, so isn't a government secret, the public knows. And about early 1918, until april, because there isn't a big US presence in Europe, there is USSR, Germany isn't totally defeated, so there is a chance to change something.