Those holding divergent political opinions - especially leaders - are often accused of being deceptive and "liars."
Whenever used, this word has particular power to brand someone as morally untrustworthy or as attempting to deceive with malicious or selfish purpose. Those who label someone as liar almost always (a) disagree with the person on other socio-political grounds and (b) insinuate fully conscious awareness of something they themselves believe is true.
One might ask, then, what exactly does it mean to be deceptive? One might be completely consciously deceptive, for instance - or only partially conscious of deception. Alternatively, unconscious deception might happen when a person is embedded in a system that shuts down full awareness.
An accusation of lying implicates the moral character of someone as being corrupt, rather than merely that person holding a different worldview than where we stand. From the latter view, striking disagreements can be scary enough as to elicit such attacks - even if they do not, in fact, reflect actual conscious deception. In this light, others might look at Obama and Bush and say, “I too disagree with their actions, but I don’t think they were lying about them or trying to be deceptive. I believe they sincerely believed it was the right course for the country - even if they were wrong.”