That's called being a two faced lier.
Cognitive dissonance requires psychological stress as a driver of change in attitude.
Politicians seem incapable of changing their beliefs, typically because most of them are narcissistic.
Narcissism, self absorption general, and a lack of empathy, better explains why ploticians espouse differing beliefs depending on who and when the audience is.
Edit: fixed a word
(Paging 'dredmorbius; I'm way past my bedtime, and he knows this stuff better anyway.)
To paraphrase Stafford Beer.
But, it's easily possible for democratic representation to result in a set of contradicting laws without any dishonesty.
Suppose laws A, B and C are incompatible, but any pair is reasonable.
35% of representatives fundamentally support A and B [and not C];
35% support B and C;
30% support A and C.
All three such laws will pass with majority support, with everyone holding true to their represented beliefs - but the system is still at fault.