Where did you get the "sufficient" part from. I read Barr's report but I didn't see that except under the OOJ part.
The OOJ part discusses a balance of evidence.
The collusion part simply presents findings. It does not discuss evidence. That can mean either no evidence or insufficient evidence, but either way, an amount such that the SCO felt comfortable drawing a conclusion about the strength of their case.
Prosecuting a crime requires establishing several "elements", all of which must be established. If you have evidence of one element but not another, then you have evidence, but not sufficient evidence. (Analogy: to make a certain dish I need three ingredients. If I have two of them, I have ingredients, but not sufficient ingredients).
You can also have evidence that supports an element but is not sufficient by itself. (I have 1/4 cup of flour and need 1/2 cup).
Conspiracy requires both an agreement and an overt act.
Here, some evidence certainly exists. For example, meeting with Russians about receiving information would be circumstantial evidence of a conspiracy, because meeting with people engaged in a criminal act about something related to the criminal act can support the existence of an agreement in furtherance of that act.
But it wouldn't be conclusive, because that meeting could happen without making an agreement. Or they might agree, but it still wouldn't show an overt act. So a prosecutor would have evidence of conspiracy, but wouldn't find that
sufficient to establish a case.
That is why "sufficient" is in a parenthetical.
When it came to collusion it was straight forward in saying that not only did they not collude with Russia they refused Russia's help multiple times. Which is something I see left out which is pretty important if you ask me.
I just looked at the summary and it does not say anything about refusing help.
That's probably why I left it out.
It says "the Special Counsel did not find that the Trump campaign . . . conspired or coordinated with the Russian government . . . despite multiple offers to assist . . ." Thus, we have multiple offers of help, but nothing on rejection or acceptance. You can choose to infer that rejection, but it is very clearly absent.
We do have a lack of conspiracy, but that, as above, requires an agreement
and an overt act. Saying that there was no conspiracy only tells us that at least one of the above was missing. Coordination, which was defined as an "agreement . . . on election interference" without an overt act - also does not require a rejection to fail.
Note: edited on distinction between coordination and conspiracy.