The cosmic order is known as Rtam.By the term " sanatana dharma" , we refer to the vedic dharma as interpreted and practised by Rshis from time immemorial. It is one without any Adi and anta.
" tasmAt dharmam paramam vadanti " - Tai Upa
When we understand the truth " sarvam khalvidam brahma", the entire creation including the cosmic order is of the form of the Supreme.
SrI RAma is the embodiment of dharma
"RAmo vigrahavAn dharmah *.
Though we know that the Supreme has created the canons of dharma,as it is meant for adherence by the people at large voluntarily on their own, it is preferable to call it as sanAtana dharma instead of sanAtanA's dharma.