Against his wider semi-bluffing range:
Board: Tc 8s 6h Kh
Dead:
equity win tie pots won pots tied
Hand 0: 58.392% 58.39% 00.00% 668 0.00 { 8c8d }
Hand 1: 41.608% 41.61% 00.00% 476 0.00 { AA, KcKd, KcKs, KdKs, TdTh, TdTs, ThTs, 6c6d, 6c6s, 6d6s, KTs, QhJh, Jh9h, Th9h, 9h8h, 97s, 8h7h }
Against the above range and removing AA (assuming he 4b this pre):
Board: Tc 8s 6h Kh
Dead:
equity win tie pots won pots tied
Hand 0: 47.273% 47.27% 00.00% 416 0.00 { 8c8d }
Hand 1: 52.727% 52.73% 00.00% 464 0.00 { KcKd, KcKs, KdKs, TdTh, TdTs, ThTs, 6c6d, 6c6s, 6d6s, KTs, QhJh, Jh9h, Th9h, 9h8h, 97s, 8h7h }
Against only sets, straights, and KTs:
Board: Tc 8s 6h Kh
Dead:
equity win tie pots won pots tied
Hand 0: 38.636% 38.64% 00.00% 255 0.00 { 8c8d }
Hand 1: 61.364% 61.36% 00.00% 405 0.00 { KcKd, KcKs, KdKs, TdTh, TdTs, ThTs, 6c6d, 6c6s, 6d6s, KcTc, KdTd, KsTs, 97s }
Against only sets and KTs:
Board: Tc 8s 6h Kh
Dead:
equity win tie pots won pots tied
Hand 0: 44.421% 44.42% 00.00% 215 0.00 { 8c8d }
Hand 1: 55.579% 55.58% 00.00% 269 0.00 { KcKd, KcKs, KdKs, TdTh, TdTs, ThTs, 6c6d, 6c6s, 6d6s, KcTc, KdTd, KsTs }
So yeah, you have to call here even in a worst case scenario unless you think there's a 0% chance he has KTs, and even then it's still probably a call.