There are a lot of flavors of socialism, just as there are of Christianity. Socialism predates Marx; it's clearly there in the French Revolution and some attribute its basic tenants to Jesus himself (or Mazdak and the Khurramites, who I just learned about via the WCBC).
I think you can find quite a few people who genuinely embrace some form of socialism, but I'm struggling to think of an American politician or intellectual who would say they are Marxist. Do you have anyone in mind?
Marx had very specific theories about capitalism, economics, the philosophy of history, etc. that people don't understand, or if they do, wouldn't embrace.
Don't take my word for it, though. The Mises Institute agrees:
To effectively counter this brand of American socialism, it is important to properly identify the problem, and to attack with precision.
mises.org