It is an obligation of the historians to try actively to distance themselves as much as possible to what they are trying to report. They must check all the sides of the events, different sources, examine them all one by one and put in a larger context that should not be interfered by one's opinion.
The closest one is the first one. He can veto any bill and send it back to congress. He has to state why and they have to consider his whys. If both houses can must a 2/3 majority for the bill, it passes without his signature.
