Knowing that the democrats in the House are dying for anything to impeach him over, he intentionally caused problems with Ukraine which can easily be argued.
Trump may not seem smart, but I think he has set up a situation (on accident maybe, or orchestrated by someone in the intelligence community) in which the argument for impeachment hinges on evidence that can easily be manipulated to reveal his innocence. By officially being investigated in an impeachment hearing, he can “rightfully” prove his innocence and thus embarrass the democrats, and ultimately their candidates, to secure the 2020 election.
This is only an idea, but if you consider the Meuller probe, which was hailed as unbiased, independent, etc. And ultimately lead to Meuller telling Congress that Trump isn’t innocent but we cant charge him. This can easily be interpreted by Trump and his supporters as a win for Trump.
In addition, the amount of clickbait on Reddit linking to “news” articles making claims that sound as if Trump is beyond guilty and going down fast, really makes me think that this is just a propaganda game and not the last straw in a pile of criminality perpetuated by the Trump administration.