I would think it is quite possible to be a Marxist, and yet not try to nationalize the whole country, certainly not on once. To do that within a few years in a country as big and diverse as the US would take a number of years, and if not done gradually would require suspension of elections and absolute control over the army, as there would for sure be repurcussions and not everyone would go along with it.
If that is your political profile though, your Marxist leanings might show up though...say if you started in life as a community organizer, went to churches where the foundations of the government were criticized, where if you were chosen as a leader that you would choose a chief law enforcement official someone who thinks like you, so that the laws to be enforced would be chosen carefully as to when and how and against whom they were enforced.
You could demonize some big businesses and give public money to those you like, as if it is your job, and not just your agenda, to choose who wins and who loses. You could also work hard just to block the efforts of those companies who don't fit your agenda, say by preventing them from doing business in a state that doesn't fit your Marxist profile as well.
And you could nationalize some companies, the weaker ones, where you carefully avoid the established corporate law and use public funds again to infuse those funds into a weak enterprise, and win favor by giving organized labor (the key constituent to any qualified Marxist movement) a sizeable chunk in ownership.
I would also call out successful wealthy people for not paying their share to help the poor, and I would support the sit-ins and protest movements of the have-nots in order to pit economic classes against one another. If I gave a speech, I would not try to lift all boats, I would point out the differences in these groups of people, and I would point out that the government, not the people, are responsible for all of the good (and by extension, none of the bad), that happens for anyone who does well.
That's what I would do, if I were trying to extend a movement over a longer period of time. And if I got two four-year chances instead of just one, I might be able to execute my agenda better in the second term than the first one.