Anyone can have a cerebral incident from a variety of causes. No one should imply that anyone who is physically handicapped is also cognitively handicapped. Aphasia does not imply cognitive dysfunction, either. One can hear and comprehend while being physically incapable of speaking, speaking clearly or speaking without a distinctive tone that can accompany damage to the speech centers.
Senator Johnson is likely now extremely aware of how people may react to his personal presentation. I really hope Republicans are kind and understanding. Again: this can happen to anyone, at any time and until it does happen to you or to someone you know, few people truly understand what is going on physically with the affected individual.
Are you a doctor/nurse/practitioner.