You mean that he told the Australians that the Soviets were offering to collude with the Trump campaign (https://www.abc.net.au/news/2019-12-10/alexander-downer-report-may-surface-in-trump-impeachment/11782834) and you don't understand why a full investigation was opened?
April 2016, Mifsud tells Papadopoulos about the "dirt".
So Mifsud knows about Guccifer and Guccifer 2, or whatever they were.
From Horowitz, this may have very well been public information. If it is, big deal.
"It was unclear whether he or the
Russians were referring to material acquired publicly of [sic] through
other means."
It probably doesn't take a rocket scientist to come to the conclusion that a country that has been attempting to interfere in our elections might do it again if they have "dirt".
And Papadopoulos is no rocket scientist.
July 22 ? Wikileaks starts releasing emails.
On July 24 ? Mook goes on tv to say the Russians "hacked" the DNC.
We'll skip the Crowdstrike CEO saying they had no evidence that information was exfiltrated for now.
On July 26, Downer comes into play with the Papadopoulos told him that Mifsud told him story.
July 28, it gets to the FBI.
From the mentioned Horowitz report ..
"According to The Special
Counsel's Report, Mifsud only showed interest in Papadopoulos after learning of Papadopoulos's role in
the campaign, and told Papadopoulos about the Russians possessing "dirt" on then candidate Clinton
in late April 2016"
From Downer ...
https://twitter.com/i/status/1580037960954974209