I haven't proven I'm notna Marxist. There's nothing in any Marxist literature that says, "If you pragmatically vote for a non-Marxist to give the Marxist movement in your country a tactical advantage, then you are no longer a Marxist." Marx, Engels, and Lenin all talk about how it's sometimes necessary to support non-Marxists to give the Marxist movement an advantage. You'd know that if you read anything from them.