Sen. John Cornyn (R-TX) broke the race to succeed Sen. Mitch McConnell (R-KY) wide open on Thursday when he announced he would run for Republican leader this fall.

Cornyn, the former Senate majority whip, is one of the “three Johns” most likely to replace McConnell after he steps down in November. He is expected to face competition from Sens. John Thune (R-SD) and John Barrasso (R-WY), the No. 2 and No. 3 Senate Republicans, respectively.