From what I understand from all the talking heads, "quid pro quo" seems to be a construct- the most convenient one at hand for the White House at the moment- and doesn't really need to be established to underscore the severity of what's already come to light. Based on the most current reading, there seems to be a consensus (from everybody not on the right side of the congressional aisle) that a sitting president pressuring a foreign head of state to dig up dirt on a political opponent is... pretty dang bad.

As for Barr, at this point it's his word against the written transcript:

Mr. Giuliani is a highly respected man. He was the mayor of New York City, a great mayor, and I would like him to call you. I will ask him to call you along with the Attorney General. Rudy very much knows what's happening and he is a very capable guy. If you could speak to him that would be great.

Whether or not Barr ever followed up is maybe immaterial. As the head of the department that would have to work hand in glove with Congress on an investigation of this magnitude, Barr is demonstrably compromised.