Because hey, both of them are having a big month.
What do Justin Timberlake and Barack Obama have in common? Quite a bit, actually. Both are very popular among women and elite critics; both have won Grammys (yes, really); both have performed Al Green's "Let's Stay Together"; and both have had a big month, with the former releasing his first new single since 2006 and the latter inaugurating his second term in office.
To mark the occasion, here's a great mash-up of Obama singing Timberlake's "SexyBack," with Joe Biden (of course!) performing the Timbaland hypeman role.