Firstly it’s not half of America since not everyone votes. Secondly I doubt every Trump voter believes or believed every single lie he spewed. There are tons of reasons why someone might have voted for him without really agreeing with all of his rubbish. IMHO it would help to stop painting this other section of voters as dumb and easily duped.
Whether or not it's half, whether or not they really believed every word.. a majority still supported Trump such that he was elected president of the United States. How much his supporters actually believe is irrelevant at that point