Or, as others have said, his job is to do nothing, and do it well. This is not a court room, and it’s not a legal proceeding. It’s a political proceeding.
How can this venue have a presiding judge, an impaneled jury, a prosecution team and a defense team and it not be a court room. If you ask each of these whether they are in a legal or a political arena the answer you might get is that if this were a political arena they wouldn't be here. They're paid to be lawyers, not legislators. This is very much a legal venue.
Now I agree with you about the political backdrop that this arises from in that the impeachment team and the committees they stem from cannot point a single federal statute that has been violated by the President. That makes the Articles political in nature, which the Constitution allows for. And I will grant you that the line between the legal and the political in this instance is very, very blurred. It's kind of what makes this all so much fun!
Enjoy your day!