Frank is the perfect example of someone who lacks credibility. As it has been explained, he is a compulsive liar and everybody in Chicago knows it. There isn't one person in town who believes a word he says because he is not a credible source; nobody trusts him. Frank has lost his credibility because of the amount of times he has broken his word or hasn't come through with the promises he has made. Fiona sums it up perfectly in season 1 when she says "Frank doesn't have any friends. Only people he hasn't pissed off yet".