I fail to see how anyone can misunderstand that an investigation into Trump's hand picked campaign staff and administration officials might not be characterized as an investigation into him personally, but is one. Because he's the top dog.
Even if no formal charges against him have been brought, or even suggested officially, the accusations are really serious and there is evidence on the subject. Colluding with a hostile government is tantamount to treason.
Trump's response to this public accusation has been, so far, deflection and lying and obstruction. This is solid evidence to me that whether or not there is fire behind all that smoke, Trump thinks that there is.
Tom