Cue the knowing smirks.

U.S. President Barack Obama announces that Chief of Staff Bill Daley (R) is stepping down. (KEVIN LAMARQUE/REUTERS)

Not three weeks ago, Nebraska Sen. Ben Nelson — who was facing a difficult re-election battle — said the same thing.

When did this start? As best I can tell, it goes at least as far back as Watergate, when John Mitchell used it as his reason for resigning from the Committee to Re-elect the President. And we all know how that one ended up…

In all the years I’ve been in Washington, the only person I can remember sounding even remotely credible saying that was George W. Bush adviser Karen Hughes. . But you tell me; who am I forgetting?

Karen Tumulty is a Post political reporter. Follow her on Twitter at @KTumulty.