Ahead of the presidential debate between Donald Trump and Kamala Harris, Jen Psaki shares what she will be watching for on Tuesday night as the two candidates meet for the first time. Steve Kornacki joins from the big board, highlighting the stakes. Then, Kevin Madden and Neal Katyal discuss how Harris's background as a prosecutor may prepare Harris and how she should approach the crucial task of defining herself to voters. Next, Jen is joined by Representative Adam Schiff to discuss Trump's continued threats against his political opponents and its implications for the election. Later, Jen is joined by Dana Bash to discuss her new book "America's Deadliest Election" focused on the violent 1872 gubernatorial race in Louisiana and its parallels to today. Jen also breaks down the baseless, xenophobic GOP conspiracy theory that migrants in the US are eating pets - and explains why it should reinforce the perception that Trump and the rest of his party are just plain weird. Finally, Jen is joined by Jim Messina, former White House deputy chief of staff for President Obama, to discuss his work with Democracy Defenders, a new PAC aimed at combatting Trump's election lies.