It effects Trump because he hired them. It affects Trump because he also lied about the contacts with Russia. It affects Trump because he knew Flynn was lying to the American people when he asked Comey to drop the Flynn investigation.
For Trump obstruction of justice is not suggested by a single, isolated incident. Many threads are now woven into the fabric on an increasingly undeniable pattern. The firing of Phreet Bharara. The firing of Sally Yates even as she warned the White House about Flynn. Seeking a loyalty pledge from FBI Director Comey. Pressuring Comey to drop the Flynn investigation when he knew Flynn was guilty. Firing Comey when he didn’t. Publicly calling the investigation of Flynn a “witch hunt” when he knew Flynn was guilty. Trying to influence Comey’s testimony with the “he better hope he wasn’t taped” tweet. Most recently he tweeted that he fired Flynn because he lied to the FBI, so he clearly knew about it then.
And yes, I actually I know all that stuff. And so do you.