Tamara Keith: The Associated Press is at the core of the pool -- that is, the group of reporters who have been following the president around wherever the president goes, going back to FDR. And the White House, by going after AP for an editorial choice, is going directly at the First Amendment. It is going directly at the freedom of the press. And it is not coincidental that they are going after AP. AP is extremely influential. They're also kind of straight down the line. They are not a partisan news outlet in any way.