I think that I understand "diplomatic immunity." But the information that I am struggling to find is...can a US President, for example, go to a host country, in which action A is legal but illegal in America, and perform said action A without consequence from the sending state, America???? I would think that there is some clause that says US officials with diplomatic immunity cannot go around breaking US law in other countries just because it is legal in those receiving countries. What is the story here????

ANYONE who travels abroad is subject to the laws of the country in which they find themselves, NOT the laws of their country of residence.

However, the US President, like other political and diplomatic officials, would probably enjoy diplomatic immunity from the laws of the nation he's visiting.

Understood, but aren't the President and most/some US officials held to some standard when abroad? It makes sense to me that a normal citizen must only abide by the laws of the country that they are in; however, a US President should be held to American law as well when abroad, at least in my opinion. But, is that the case?