Reagan never went to church on Sundays while in office. Just saying.
Sitting Presidents rarely do, it's far too disruptive to church services to have the Secret Service crawling all over the church.
Church attendance for Presidents has usually been for show. Which is a violation of the New Testament mandate to NOT make a show of it.
Reagan spoke publicly and eloquently (and humbly, which would probably cause Donald to choke) of his personal faith in Christ on numerous occasions.