A tale of two campaigns is emerging ahead of the first face-to-face meeting in the general election between President Donald Trump and former Vice President Joe Biden Tuesday night on the presidential debate stage. ABC's Martha Raddatz offers her unique perspective, having been the only person to have moderated past debates with both of these candidates. Plus, FiveThirtyEight’s Galen Druke on whether the debates have a real impact on polling or at the ballot box.  Guests: ABC's Martha Raddatz, FiveThirtyEight's Galen Druke