WASHINGTON (AP) — Mitt Romney's vice presidential search has entered a new phase: auditions.

As his campaign evaluates potential running mates, Republicans with a possible shot at the No. 2 spot are starting to engage in unofficial public tryouts for the traditional vice presidential role of attack dog.

Such possible contenders as Florida Sen. Marco Rubio and New Jersey Gov. Chris Christie have had scorching words for President Barack Obama.

Not that any of those who may have landed on Romney's list are talking about becoming vice president. Nor are they acknowledging that they're trying out for the role or saying they've been asked to do so.

Top Romney aides are sworn to secrecy, as are potential running mates and their staffs — an example of the Romney campaign's closely controlled, no-leaks culture.