The entire premise of the movie relies on the idea that being elected President of the French Republic enables you to choose your own government and pass any law you want. While Emmanuel Macron works very hard to give this impression, this is not true at all. The real power or the French Republic lies in the National Assembly, which can overthrow the government and decide the laws to pass, entirely sidelining the President and tuning him/her into not a mostly ceremonial figure, as the cohabitations (i.e. a President from Party A, but a government from Party B) under François Mitterrand and Jacques Chirac have shown. In real life, a newly-elected President facing a hostile parliament would have to immediately start campaigning for the legislative elections (usually less than two months after the runoff these days) to make sure they would have a majority of députés (congressmen) in the National Assembly with which they would rule the country (the députés can even override whatever the Senate sends their way). A President suddenly changing their minds about their ideology would certainly not sit well with their electoral base nor with the backing political party, and all this would make for a particularly interesting election cycle.