Is it okay for any current President of the United States to ask a leader of a foreign nation to investigate a political opponent/rival? Any President, regardless of party.
The treaty you cite is irrelevant. The abuse of power is the President asking the foreign leader to do it whether or not there was a quid pro quo. I happen to believe there was, but we will have to see what the evidence shows....(although Mulvaney explicitly admitted there was on Fox News)
So... can you give a straight answer to the hypothetical question. Please don't give me the "there is no point in answering a hypothetical question".