You convinced the smooth-talking politician Bill Taggart to tell the truth in public.
As you progress through the story you'll need to confront Taggart about his wrong doings at the Convention Centre. For this achievement you MUST walk in on his conference and not sneak into the building and then his room. If you sneak into his room and find the evidence via his computer, this achievement will then be void as well as the 'The Last Straw' achievement later on. So to obtain these you'll need to get the evidence from his mouth only!
The problem sometimes with this dialogue challenge is the replies from him can change even if you reply with the same answer or question. So make sure you save before you walk into the room. If have the Social Enhancer upgrade (CASIE - Which you should have), this may become a bit easier. If you follow the answers and video below you shouldn't have any issues with this achievement:
You have to realize that the same options won't work everytime. Conversations change. Easiest way to get any of these achievements is save before you talk to anyone and take the speech aug and figure it out yourself. It's not hard if you have the speech aug. If you fail reload a save and try again.