Mike Johnson flies same Christian nationalist flag outside his office that Samuel Alito flew at vacation home

They know the meaning. Most of the ones I grew up around chose to believe that since "separation of church and state" doesn't appear in the Constitution that it was a fringe idea a couple of the founding fathers had, that "liberals" today have made into a bigger deal than it should be so they can keep "persecuting" Christians.

Christian nationalism takes all the dogmatic thinking they have about the Bible being instructions from an infallible, all knowing God, that must be followed, and applies that thinking to the US Constitution and the founding fathers. Once you're in the mindset of reading something like it's absolute truth that can't be questioned (at least the parts that tell you you're wrong, the parts that say I'm wrong are different), it's easy to get stuck in that mindset for everything you read.