The "leader of the free world" stops being coincident with the officeholder of the US presidency the instant someone devoid of positive leadership qualities steps into it. It is entirely possible that there no longer is a "leader of the free world" now, or that it might change hands on an ad hoc basis, depending on who was particularly brilliant on a given day.

One might be able to make a case for Angela Merkel or (metonymically) Brussels, Belgium, in it's role as headquarters for NATO and host of the EU parliament, but I'm inclined to believe the title is still awaiting someone worthy of it.