As the Jeremiah Wright scandal was breaking, I speculated that trouble of this sort for her rival was precisely the reason Hillary Clinton was staying in the race for the Democratic nomination — that the longer the primary season extended, the more chances there would be for Obama to stumble, and that she would be there to seize the baton and run for the finish line. But of course, the longer the primary season, the more chances there are for Hillary Clinton to stumble as well. And the difference between Obama and Clinton is that he can stumble and still win because he’s in the lead. She can’t afford to stumble at all if she is trying to gain on him.

And stumble she has. Her bizarre lie about the nonexistent sniper fire that threatened her in Bosnia was the first nail. The hurried departure of her chief campaign strategist, Mark Penn, is the second. It makes perfect sense that Penn has been defenestrated for doing something entirely sensible — meeting with representatives of a U.S. ally, Colombia, that wishes to pursue a closer trade relationship with us. Colombia is not only a friend of the United States; it is engaged in a battle with the worst player in the Americas, Hugo Chavez’s Venezuela, which is trying to destabilize it. But because Hillary is engaged in a gross act of deception toward Democratic primary voters on the matter of free trade — which she has decided to oppose solely for P.T. Barnum reasons even as she would surely support it for every good reason once in the White House, — Penn had to go and go fast.

Whatever kind of error this was — Penn’s for taking the meeting, Hillary for employing Penn, or Hillary for chucking Penn out the door now when she might have done it more profitably two months ago once it became clear his strategy for her nomination had failed utterly —  it’s one error too many for her. How can she make the case that she is a better candidate in the general election than Obama if she can’t go five days without making a major blunder on the campaign trail?

She can’t.