At last, a clue. 

The rollout of headline speakers for the Republican convention offers the first bona-fide signals from the Romney campaign over who's on the short-short list to be his running mate. 

It's probably safe to say that the seven major speakers announced overnight will not be Romney's vice presidential pick. Those speakers are: South Carolina Gov. Nikki Haley, New Mexico Gov. Susana Martinez, Florida Gov. Rick Scott, former Secretary of State Condoleezza Rice, Arizona Sen. John McCain, former Arkansas Gov. Mike Huckabee and Ohio Gov. John Kasich. 

Now, speculation can focus on who's conspicuously absent from that list as the Republican presidential candidate prepares to unveil his nominee likely before the Tampa convention, to be held Aug. 27-30. 

Those not on the list, and presumably in the running for running mate, include: Florida Sen. Marco Rubio, Wisconsin Rep.