PHILADELPHIA — Sarah Palin made a trifecta of historical stops in Pennsylvania on Tuesday, hitting the Gettysburg battlefield, Independence Hall and the Liberty Bell as part of a secretive bus trip that has some wondering if she’s trying to drum up publicity for a 2012 presidential run.

The former 2008 vice presidential candidate and her aides refused to share basic details about the “One Nation” tour, which started in Washington and was expected to take her to New England in the days ahead.

With security tight and some roads closed off, Palin toured Independence Hall in Philadelphia before working her way across the street to the building that houses the Liberty Bell.