Disclaimer: I couldn't open the link so didn't read the article, but I can't imagine the underlying story being much different from all the others.
I really don't understand how anyone can consider this an issue worthy of consideration, let alone litigation.
In what possible way does it matter and how will anything material change if the phrase is forbidden?
It's not as if the President is taking an oath to govern in accordance with religious teachings.
These gadflies are kooks and/or publicity seekers.