I yield to no one in my disdain for President Trump. And I certainly have no brief for Manafort, who has been accused of laundering tens of millions of dollars from sources connected with Russia and the Ukraine. Thus my overall assessment is that Manafort has some significant legal exposure and that, given his role in the Trump presidential campaign, that exposure is of concern to Trump and of interest to the special counsel.
All that said, I think that the special counsel's allegations of witness tampering are rather ... thin. The
FBI agent's declaration in support of the allegations is long on detail about what Manafort and the "Hapsburg Group" did before the elections and short on information about the tampering allegation itself. Drill down into the exhibits and you will see that only one,
Exhibit N, is evidence of communications between Manafort and the witnesses he is alleged to have contacted in a tampering effort.
Study that exhibit and you will see that Manafort was successful in speaking to one witness (Person D1) for exactly 1 minute and 24 seconds. He attempted three other phone calls that did not connect and he sent two WhatsApp messages—one a link to an article describing his indictment and the other saying "we should talk." When asked about the contents of the conversation with Manafort, according to paragraph 14 of the FBI declaration, Person D1 said that "Manafort stated that he wanted to give Person D1 a heads-up about Hapsburg" and "D1 immediately ended the call because he was concerned about the outreach."
And that's it. Really. The other part of the allegation is that someone else, Person A, reached out to Person D2 and told D2, in a series of texts that "P" (presumably Paul Manafort) was trying to reach D1 to brief him and that "Basically P wants to give him a quick summary that he says to everybody (which is true) that our friend never lobbied in the US, and the purpose of the program was EU." A month later, Person A reached out directly to D1.
https://www.lawfareblog.com/manafort-tampering-allegations