Philadelphia (AFP) – President Joe Biden, Democratic superstar Barack Obama and Republican firebrand Donald Trump all converged Saturday on Pennsylvania to push their parties to the finishing line in a race Biden said marks a “defining” moment for US democracy. The battle of the serving and two former presidents marked the start of a final crescendo before Tuesday when Americans will decide who controls Congress during the last two years of Biden’s first term. Polls put Republicans well ahead in the fight for the House of Representatives and also show them gaining momentum in the Senate races …