Is it possible for the teachings and rulings of Islam, such as the ruling on adultery, to be distorted? And is it possible for the Sunnah to be distorted, such that a rejected hadith is thought to be authentic?

It is possible for someone to declare lawful what Allah has forbidden, or to forbid what He has permitted, or to weaken an authentic hadith, or to strengthen and rely upon a fabricated hadith. And they may find listeners among deviants or those with weak faith. However, Allah has guaranteed the preservation of His religion, and whenever a deviant or an atheist appears, Allah ordains someone to expose them and clarify their misguidance.