If I were Trump, I would nominate Merrick Garland right now.
As I would say, that would be "an effort to bridge the deep divide in ths country; and Judge Garland is the best judge who is not yet a member of the Supreme Court."
Moreover, this is to show that the President is the one that holds the power, instead of scheming senators. And for those who think he is too left-wing: he is 67 years old. Not everyone has the stamina of Ruth Bader Ginsburg.