The principle goes once someone has broken your trust, whether by unfaithfulness, stealing or violence, they are usually like that generally and would do it again more likely than not.
Just after becoming elected he made CO2 a pollutant. The dictionary definition is 'A noxious substance which has found its way into the environment and needs to be removed'.
Therefore, Barack Obama, a lawyer who learned definitions in his first year of college, has just lied to you. If CO2 was a pollutant we'd want to remove it entirely from the atmosphere which by his own definition is the only end for all pollution. There are no degrees or levels of pollutant, it is an absolute term, much like pregnancy. He further dismisses the carbon cycle and the fact if we don't breathe a certain amount we'd die as fast as we would without oxygen.
He doesn't stop there, they never do. He also refers to nuclear radiation as 'clean energy', but would not visit Fukushima to demonstrate how clean it was when he had the opportunity.
Regardless of your belief in climate change or otherwise, Barack Obama is a liar on at least these two occasions. He has openly stated falsehoods and as a result should never be trusted on any issue whatsoever as he is a simple cheat.