You said in your traditional rhetorical style: "How accurate was the CBO in scoring the ACA?"
Translation: The CBO was not accurate in scoring the ACA. This, if they were not accurate in scoring the ACA, they could not be accurate now.
The root principle is that if a group had been inaccurate about something before, they are not or at least very not likely about a new related prediction. 
Do you believe in the principle that one should not trust the future predictions of a group that made a poor prediction about the same thing in the past?