In fact, even if some one were a paid member of the campaign staff there would be nothing wrong with talking to the Russian ambassador.
Very true.
The entire scandal has two weak points for the GOP.
Sessions traveled to the GOP Convention on campaign funds. Not illegal, but it limits what he can do while at the convention. It appears that Sessions was approached by the Russian Ambassador, not the other way round, so he can't be held responsible for it.
The other issue they seem to be making dog shit about is the fact that while being vetted by the Senate, he did not admit to having spoken to Russian officials in any capacity. So, an issue has arisen regarding why he did not go back and correct the record afterward? Every nominee does it because no one can remember everything all the time and information left out of a Q&A can be amended into the record; even the Democrats do this.
So, then it becomes a matter of the questions he was asked. If the idiot from the Democrat party asked his questions about Russia in regard to Sessions being part of the Trump campaign, then Sessions had no real reason to go back to amend the record because he did not lie about his not having conversations with Russians on behalf of the Trump campaign, even after the election. He was never a member of the Trump campaign.