You can still get tickets to the show, but as of Sunday morning, just two premium balcony seats remained, and general admission floor tickets were up for resale at a 131% markup.
Voters are increasingly breaking with the Republican and Democratic parties. One national poll found a record 45% of Americans consider themselves politically independent.
The forum is set to start at 6 p.m. Monday at Resurrected Life Church in Center City Allentown.
Democratic voters in Pennsylvania's 16th and 18th Senate districts may have contested races this spring. Meanwhile, Republican Zach Mako is seeking re-election in Pennsylvania's 183rd House District.
In his first public performance since the "American Idol" episode with him on it aired, Allentown singer Seth Witcher on Thursday was cagey about his status on the show.