Every president ends up disgusted with the news media in general and with certain individuals or outlets in particular.

But there's an old adage, often attributed to Mark Twain, that advises against picking fights with people who buy ink by the barrel.

He was speaking of course of the big media of his day, which were newspapers. Most presidents refrain from directly attacking particular media outlets, perhaps with that adage in mind or perhaps mindful another old saying, that it's a bad idea to get into a public fight with someone smaller than you are, because it diminishes you and elevates your opponent. Fox News may be the biggest news channel by far, but it's not as big as the presidency.

There's an additional problem in fighting with the press. The vast protections afforded by the First Amendment make the media largely invulnerable to attacks from politicians. For all these reasons, the kind of salvos recently fired at Fox News from the Obama White House represent a risky strategy.

The White House has chosen its words with some care, note the characterization of Fox not as conservative, but as Republican. A lot more Americans identify themselves as conservative than as Republican. What's more, if Fox News really were a GOP mouthpiece, the White House would not be attacking it. It would feel no need to.

Brit Hume is the senior political analyst for FOX News Channel.