Joan Baez sang at Woodstock. If you recognize either name, you probably already knew that. If you don’t, go to Google, then come back and help us puzzle something out.

Why would the Army be afraid of her?

Last Friday, John Mellencamp gave a concert for injured soldiers at Walter Reed Army Medical Center. Ms. Baez, a friend who’d been invited by Mr. Mellencamp, did not. She was barred by Army brass, supposedly because of the lateness of the invitation, although Mr. Mellencamp’s camp suggested it was because she was considered objectionable.

Objectionable for what? To whom?

Mr. Mellencamp and Ms. Baez are both politically outspoken. Both have denounced the Iraq war. Yet Mr. Mellencamp’s activism is the kind the Army could more easily overlook. He wears a T-shirt and jeans and sings songs so down-home, so red, white and blue, that you could use them to sell Chevy trucks, which Mr. Mellencamp has actually done. “Let’s forget about any problems we might have and let’s just have a good time,” Mr. Mellencamp told his audience in what The Washington Post reported was a rousing and apolitical show.

Although Ms. Baez is as much of an activist as ever  she camped in a tree last year to stop the bulldozing of an urban farm  she would probably have shown similar tact. In a letter in The Post yesterday, she said she regretted not having given soldiers a better welcome home from Vietnam, and would have loved to sing at Walter Reed.