They will pledge loyalty to the POTUS
Bad idea. The oath is to "support and defend the constitution" for a reason. We don't have a monarchy. A loyalty oath to POTUS competes with the constitutional oath should a conflict arise.
First place to start cleansing is to remove all Dual Citizens and all who have competing oaths like the Freemasons, Knights or whatever fraternity because they're privileged systems of cronyism that seek unfair advantage.
You can't serve two masters.