This is the second performance as a government lackey I have seen and unfortunately this is the distant second from Gian Maria Volontè in Investigation of a Citizen Above Suspicion. Trintignant does seem to randomly try to play the part in different ways, but unlike Volontè's work there is not an underlying purpose to this. Trintignant does not seem to know how to play the part, and does not even know how exactly to play the different approaches he decides to take. Trintignant often plays the part as the silent killer sort, sometimes just a non-entity, sometimes just a man who is pushed around by others, and sometimes an emotionally sensitive man. This would be fine if he went from one to another in a character arc but that is simply not the case.
Trintignant often is the non-entity who sits in rooms and listens to other speak. I will admit it is a difficult trick to make such a character interesting but it can be done, Gary Oldman in Tinker Tailor Soldier Spy is one example. Trintignant seem thoroughly out of his element here as he is a non-entity as the character of Marcello, but he is also a non-entity when it comes to the film itself. He never has the right magnetism to draw you in to his performance, even though he does not seem t be doing something. There is not anything that Trintignant conveys in these scenes, he just seems to sit there and allows for Bernardo Bertolucci's direction to be the only star of the show.
Marcello is often a protagonist pushed around by the actions of others, not unlike the titular character in Bertolucci's later film The Last Emperor. Trintignant does nothing in terms of showing how this treatment affects Marcello in anyway, something John Lone did so brilliantly in that later film. Marcello changes for sure but not in the proper way as he just seems to go from one way to another, then another without the proper connection. One of the great aspects of John Lone's performance was that he portrayed the effort in his character that showed the way his character was changed by the way he was oppressed around him. There is none of that with Trintignant making every change in Marcello seem random in nature.
Of course there is the silent killer that shows up, and this probably Trintignant excels the most as Marcello but it still does not really work. For one thing Trintignant comes to it so haphazardly as he will sometime become an emotional fellow for no foreseeable reason, and Trintignant plays this version of Marcello as most just a whiner. This without a doubt takes away considerably from the cold Marcello, but as well there is nothing compelling in his performance. Trintignant is cold, but nothing more in his portrayal of Marcello and even his coldness is too simple. It is nothing like Edward Fox in The Day of Jackal where there was a striking soullessness in performance, there simply is nothing notable Trintignant brings to this killer.
Trintignant's performance in this film is almost entirely a failure in finding the right tone to set for his character. He never knows how to play the character of Marcello in the film, which is a shame as the character in the right hands could have easily been a great one. Trintignant never seems to find a grip on this character, instead trying many different ways to play him without the right rhyme or reason to it. It is only made worse by Trintignant inability to make any of the different attempts at a character particularly interesting either. His boring man who gets pushed around is too boring, his emotional man is too whiny, and his cold man just is not cold enough.