An extreme tendency to see the best in a person/phenomenon, or to turn a blind eye to the (potentially) negative aspects of a person/phenomenon.
His fervent belief that the US judicial system, as currently constituted, will act as an effective curb on the excesses of #47's administration, comes across as a case of hyperpollyannity.
The extreme tendency to adopt a positive view/opinion of a person/phenomenon, or to turn a blind eye to the probable negative impact of a person/phenomenon.
Their view that the US judicial system, as currently constituted, will be sufficient to curb the excesses of #47's administration seems like a case of hyperpollyannity.