It follows rather directly. For it to be high treason to be against sending more military resources to Ukraine would mean that either the representatives are members of the Ukrainian government or, as was implied here, that Ukraine is a puppet state.
It's not high treason against the USA to be against the USA sending military resources to another country. You can only commit high treason against your own country.
That's a false equivalence, this isn't exactly cooperation towards a mutually beneficial goal, this is just trying to reduce support for a country which by sheer coincidence is an enemy of Putin.
You say that US citizens (the republican politicians) who do not support Ukraine should be trialed for treason. This implies that Ukraine is a part of the US, doesn't it?