Wanted: A public servant who will pledge to keep America safe in a world that is fundamentally, relentlessly, hide-under-your-bed dangerous. Must have cool temperament, intestinal fortitude. Will receive much criticism, scant praise.

Any takers?

Janet Napolitano will step down in September from her post as secretary of the Department of Homeland Security, which might be considered the worst job in politics by anyone with a nervous system and a healthy sense of cowardice. If it's not the worst, then it's the most perilous and unsung.

It's "one of the toughest and most thankless jobs in Washington," Sen. John McCain, R-Ariz., said in a statement about Napolitano's resignation.

"Everybody knows when you've messed up, but nobody knows when you've done a great job," says Amy Walter, national editor of the Cook Political Report. "It seems all you can do is lose. … When you think about most of the Cabinet positions, they're relatively thankless, (but) it seems at this job you're almost guaranteed to be a lightning rod."

DHS secretary is the youngest Cabinet-level job - formally established by Congress in late 2002 in response to the Sept. 11 terrorist attacks - and yet it's also one of the most expansive and fraught. The secretary's portfolio includes terrorism, natural disasters, cybersecurity and widespread medical crises. So, worst job, right?

"I've said it!" Tom Ridge bellows on the phone.

Why, sir?

Congress, Ridge says. And Congress' involvement in the dozens of agencies within the department.

"The relationships that the secretary has with multiple committees and jurisdictions on the Hill complicates his or her life," says Ridge, who served as the first DHS secretary, from 2003 to 2005.

Ridge's successor, Michael Chertoff, has heard the "worst job" comments before and thinks they're "somewhat exaggerated."

But DHS secretary is certainly one of the most challenging in politics, he says, because of the broad mission mentioned by Ridge. "If you're temperamentally an anxious person, or a person who has difficulty making decisions, this is not the job for you."