In an article on why it's wrong to call someone whose accuracy is deeply questionable a liar is out of bounds, Daniel Henninger of the Wall Street Journal goes full Godwin:

The Obama campaign's resurrection of "liar" as a political tool is odious because it has such a repellent pedigree. It dates to the sleazy world of fascist and totalitarian propaganda in the 1930s. It was part of the milieu of stooges, show trials and dupes. These were people willing to say anything to defeat their opposition. Denouncing people as liars was at the center of it. The idea was never to elevate political debate but to debauch it.

The purpose of calling someone a liar then was not merely to refute their ideas or arguments. It was to nullify them, to eliminate them from participation in politics. That's what is so unsettling about a David Axelrod or David Plouffe following accusations of dishonesty and lies with "whether that person should sit in the Oval Office." And that is followed by President Obama himself feeding the new line in stump speeches without himself ever using the L-word.

For those who are new to the idea, Godwin's law has it, on one corollary at least, that one loses an argument as soon as one compares one's opponent to Hitler.  What's ironic about this employment of it is that there is a much easier argument against the "liar" accusation: it's not true. 

Sadly, that is a road Mr.Henninger has not taken.  He can't, of course, because that road is closed.