They have been shadowboxing at separate campaign stops across the United States for weeks but the Democratic and Republican leaders find themselves on the same battlefield Saturday as they make closing pitches in Pennsylvania for next week’s midterm election. President Joe Biden will rally alongside his old boss Barack Obama as the Democrats deploy their big guns to build the energy they hope will spread nationwide and reverse the late rightward-shift in polling. And in a split-screen preview of a potential rematch of the 2020 presidential contest, the midwestern state is also playing host to Biden’s predecessor and bitter political rival Donald Trump. Obama — still the party’s most bankable star six years after leaving the White House — begins the day in Pittsburgh with Democratic candidate John Fetterman, who is in a dead heat against Republican TV medic Mehmet Oz in their crucial Senate race. Biden and Obama then appear in Philadelphia, the historic cradle of US independence where the 44th and 46th presidents will woo voters from the suburbs that make for a crucial base of Democratic support. The Keystone State backed Trump over Hillary Clinton for president in 2016 but preferred Biden to Trump in 2020.