ABC News anchorman tells The Page one serious reason and one less-serious reason to tune in. Watch video above.
Gibson and George Stephanopoulos ask the questions in the 90-minute one-on-one face-off starting at 8 pm ET at the National Constitution Center in Philadelphia.
A full 90 minutes of debate time -- not counting introduction, commercials, etc.
Debate is first of entire campaign to be aired during weekday prime time on a broadcast network.
Check back after the debate for Mark Halperin's report cards covering each candidate's substance, style and more.
