Believing anything from Politico was your first mistake.

In Sussmann’s case, prosecutors asked Cooper to rule in advance of trial that Sussmann was “acting in concert toward a common goal” with the pro-Clinton operatives, researchers and others. Such a ruling would have given the government attorneys more latitude to introduce emails against Sussmann, but the judge said the scope and membership of the alleged anti-Trump venture was too uncertain to make such a finding.

• To clarify for you, Typically prosecutors can ask to judge to make a premature ruling when the evidence being ruled on is not illegal. Because Hillary being apart of this conspiracy could be illegal, there would need to be more hard evidence, a premature ruling couldn't fit here. which is a good thing, you would never want a judge to prematurely rule against you in a criminal matter without ever getting your day in court.
• Because he isn't charged with conspiracy, they need to limit evidence to what he is charged with or else you get two trials in 1.
• Once he is charged and convicted, with doing something illegal he can then be put onto a separate trial of conspiracy if they choose to pursue that.
• You are right, only his current crime alone is what's being looked at for now. But like a domino, once you prove one thing, he can go to trial and charged for another crime afterwards. Its possible, that they cannot put him on trial for conspiracy yet without first proving what he was doing was illegal. I am not a legal expert.