Roberts running, plus Antonin Scalia's death, creates two open Supreme Court seats that Mitch McConnell can hold hostage for a year (or more if Clinton wins). Fun.
A chance to get a 6-3 liberal Supreme Court (Clinton likely isn't going to keep the Merrick Garland nomination to replace Scalia, and she'll nominate someone relatively left-wing to replace Roberts as Chief Justice) turns out Democrats on a massive scale, allowing Clinton to win easily despite the email scandal coming out.
Former Secretary of State Hillary Clinton (D-NY)/Senator Tim Kaine (D-VA) 54%
Former Chief Justice of the United States Supreme Court John Roberts (R-NY)/Governor Brian Sandoval (R-NV) 44%