If you are on a pleasant walk and someone comes out of nowhere to demand that you stop and turn around, you may regard him as an unwelcome interloper. Until, that is, you learn that he's saving you from going over a cliff. In that case, you might realize that a real friend is someone who tells you the truth even when it isn't welcome.
That's the position of Paul Ryan as he undergoes a frenzy of flagellation from Democrats outraged by his Medicare plan. President Barack Obama's campaign has a new ad accusing Ryan and Mitt Romney of a scheme "ending Medicare as we know it." But the real enemy of Medicare "as we know it" is not Ryan. Instead, writes Steve Chapman, it's arithmetic.