The Kentucky Republican said he would finish his term as leader, which runs through 2024, and in the Senate, where he was elected to serve through 2026.
Two episodes, where the Republican senator froze and did not respond to some questions, may be symptoms of a serious illness, according to neurologists not involved in his medical care.
Demaryius Thomas had C.T.E. when he died in December at 33, but the posthumous diagnosis alone does not explain what role football had in the charismatic N.F.L. star’s quick decline.