Sarah Palin’s “One Nation” Bus Tour launched Sunday, but is it an unofficial exploratory phase for a potential 2012 run or is it a Palin family vacation stopping in historic sites in the Northeast? The answer may well be both.

According to a source with knowledge of Palin’s operation and thinking, keep a careful eye on how long the tour lasts, because it is intended as a way to test the presidential waters. If the road trip ends abruptly, it’s a sign she didn’t get the enthusiastic responses she believes she needs to launch a campaign. If the tour heads to regions outside of the Northeast like Iowa and South Carolina that, the source says, is a “big indicator” that Palin will pull the trigger.