David Brock is a political operative and founder of Media Matters, a left-wing think tank.
Media Matters is centrist, corporatist think tank. Calling David Brock or anything affiliated with him left-wing is laughable. Anyone making the claim Media Matters is left-wing is either ignorant or engaged in propaganda.
As to the larger point of your article — which is, of course, entirely undermined for lacking credibility when you include counterfactual statements such as the above — who cares? If The People want to protest Trump for perfectly valid reasons and if Soros also wants The People to protest Trump for his own pet reasons, so what? The People should still protest. They have valid reasons to do so.