Thinking Republicans (there are a few!) know the first three charges are bogus, meant to undercut loyal dissent and honest debate. The fourth charge - the charge of relativism - has a way of sticking. This is a mistake.
Oh, sure, there are some relativist among non-thinking Democrats (yes, there ae a few!) but for the most part liberals are pluralists, not reletavists.
Here, for example, is Martin Peretz, a liberal, quoting favorably a remark made by Yo-Yo Ma about Larry Summers, also a liberal, who was recently dismissed from his post as Harvard's president essentially for failing to kot-tow sufficiently to the relativists and non-thinkers on Harvard's faculty.
What I like about Larry," said Yo-Yo to me on the phone from a Silk Road program in Charlottesville, Virginia, "is that he understands that nobody knows everything: not he, not you, not me. But he also understands that one cannot have a coherent view of the world without trying to know what the other knows. Larry's is an analytic mind, and yet he makes so much room for the cultural and emotional sphere, even the irrational--that which is ultimately human.Striving to know what the other knows, and striving to synthasize it with your own knowledge. This is the essence of pluralism, the rest is commentary.