Alex Wong, Andrew Harnik, and Kevin Dietsch/Getty Images
- Mitch McConnell is stepping down from being Senate GOP leader after more than 17 years in the job.
- The race to succeed him is already on, even though senators won't decide until November.
- Sens. John Thune, Rick Scott, and John Cornyn are already campaigning for the job.
Mitch McConnell's reign as Senate Republican leader is set to end next January, capping off what will ultimately be an 18-year tenure — the longest of any Senate leader in American history.