BGod
G.O.A.T.
For Federer to have a chance to be #1 again, he needs to either have Nadal not win the USO or to have a 2011 like kind of dominance during the indoor swing which I think is quite unlikely. Nadal's never been a great performer post USO which should play in Federer's favor, but Federer's form is quite questionable at the moment so who knows how many points he can really collect. If Federer doesn't claim back #1 at some point this year then I don't think it's happening ever again. An aging body, tons of points to defend in 2018, hate to pronounce the "R" word, but we're getting closer to that every day.
Basel & Shanghai would get him 300 back. Assume Nadal plays China & Shanghai and nabs like 600 points so he's still 900 ahead. Fed opts to play Paris and makes final to get back to 300 back. Then all he has to do is better at WTF.