These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Designated Hero: The film treats Dave, Ellen and Duane as heroes despite - or because of - the fact that by not denouncing the substitution they subvert democracy and the US Constitution, effectively depriving the American people of the government they voted for.
To be fair, Dave's participation in the plot is helping an Evil Chancellor. He just wises up a little later than he should have.
The film certainly portrays Dave Kovic’s move from being Bob Alexander's pawn to acting on his own account as an improvement – but morally Dave actually becomes worse when he moves from being a subordinate participant in a criminal conspiracy to being the boss of it. In a democracy, people vote on the understanding that if the person elected becomes ill or dies his successor will be appointed according to laws agreed in advance, in this case the US Constitution. Dave Kovic was not elected by anyone, nor was he in the line of presidential succession. Dave's action in usurping the privilege of the president to advance changes to policies and laws merely added to his crimes. That he thought he was "doing good" by those policies is irrelevant, in the same way that overturning the result of an election by vote fraud does not become less of a crime when the people doing it genuinely believe that the candidate they put in place by fraud has good policies.
Dave kept up the deception because he thought the VP was mentally ill and therefore ill suited for the job. Once he realized that was not the case and there was no reason for him to stay in charge, he left the job.
Fridge Brilliance: The DesignatedHero and ProtagonistCenteredMorality tropes that are brought up on this page are actually justified in-universe: early in the film, Alexander describes to Dave why what they are doing is not wrong. It all comes down to intentions: if you aren't hurting anybody, and everyone stands to benefit, then the law can be ignored (the specific argument used is, if you were driving down a road with your deathly sick mother and came to a red light where no traffic was present and you knew it was totally safe, would you run the red light? The comparison becomes valid later on, when Alexander's and Mitchell's extensive illegal actions come to light. Essentially, while Dave's actions are no less illegal, they are more moral and rightous. Whether or not this is a bad thing in and of itself is up for debate, but when held up against Alexander's actions, it's the superior choice.
Fridge Logic: At the end of the movie, the recently-widowed First Lady starts up a romantic relationship with Dave, a man who looks a lot like her deceased husband, and can't account for his whereabouts over the past few months. You think that might make people a teeny bit suspicious?
Eh, people will assume she's also an impersonator.
They might also assume it's something to do with her grief over the death of her 'beloved' husband; a bit unusual, perhaps, but not outside the realm of possibility.
Memetic Mutation: "I once caught a fish this big!" and "we're walking, we're walking".
Protagonist-Centered Morality: When the White House Chief of Staff and Communications Director conspire to replace the incapacitated president with an impersonator in order to pursue their own agendas it is a nefarious conspiracy. When the impersonator himself, his new squeeze the First Lady and a Secret Service agent do the same thing it is portrayed as heartwarming and principled.
It kind of helps, however, that the Chief of Staff is doing so for venal and self-centred reasons (in addition to his own corruption, he's basically trying to manipulate the situation so that he ends up as President) while Dave and his friends are doing so with selfless motives and to make the world a better place.
Arguably Dave's more selfless motives make his crime greater, on the grounds that someone taking over as president by false pretences because Utopia Justifies the Means is more dangerous to the principle of democracy than the same being done by a self-admittedJerkass like Alexander.
Unlike Alexander, Dave was willing to end the deception once he found out the VP was not mentally ill so it was no longer necessary for him to continue.
Strawman Has a Point: Alexander objects to Dave beginning to act like an actual president, saying, "Was he on the Trilateral Commission? Was he a senator? Was he in Who's Who in Washington nine years in a row?" Granted, Alexander is totally corrupt and Dave certainly shouldn't be following his orders, but he does have a point that Dave is probably unqualified to be president himself.
Alternatively, the point of the movie is that all you need to be a good president is compassion and common sensenote Things that are mainly denied to a major political figure due to the nature of the office, and the promises and deals necessary to get there. In other words, Dave is the perfect president because he didn't have to do anything to get there.
Even so, Dave is a great deal more qualified than the former President Mitchell because he calls in experts to help him do his job. The only reason he's able to find the money in the Federal Budget is he actually listens to his advisers while making his demands to find and cut unnecessary programs clear. Mitchell was implied to not care enough/desired to keep his hands on the reigns of power no matter what.