How do you combat this kind of ignorance?

You provide links and let people judge for themselves. Personally I have no beef with a Marxist running for President, so long as he’s not so much a Marxist that he denies he is one. That’s a short definition of Leninism BTW. Marxism is a belief. Leninism is the method of conspiracy. CS Lewis said, the Devil’s best trick is to persuade you that he does not exist.

The neatest trick of the Leninist is to regard being called a Marxist a calumny. Once past that stage, he descends into a world of code. Everyone can read the code, but if you decipher the code and call him a Marxist, you are a bigot. They have specially coded religions which are really atheisms which are empty of any religious content but their own worship of power; special versions of Democracy in which free speech is not allowed.

The real offense of a Leninist is not belief, but deceit. Their ideas are secondary. Their game is about power and in pursuit of that dishonesty, scheming and outright contempt for their audience is par for the course. Leninism is to politics what scams are to commerce. Ayers is a scammer in my opinion. You may draw your own conclusions about Obama.