Now Playing: Gates testifies against Manafort, voters turn out for primary elections

Now Playing: NY primary upset a signal to Democrats?

Now Playing: ABC News Live Update: Dozens arrested following grand jury decision Taylor case

Now Playing: Trump won’t commit to peaceful transition

Now Playing: Trump faces firestorm for refusing to commit to peaceful transfer of power

Now Playing: President Trump again refuses to commit to peaceful transition of power

Now Playing: Trump claims politics as interfering with COVID vaccine

Now Playing: Sen. Manchin will vote ‘no’ on SCOTUS nominee: ‘You've got to stand for something’

Now Playing: Trump claims White House can overrule FDA’s new guidelines

Now Playing: Trump declines to commit to peaceful transfer of power after 2020 election

Now Playing: Trump Won't Commit To Peaceful Transfer Of Power | FiveThirtyEight Politics Podcast

Now Playing: Trump Won't Commit To Peaceful Transfer Of Power | FiveThirtyEight Politics Podcast

Now Playing: 4 Senate races to watch as GOP rushes to fill Justice Ginsburg’s seat

Now Playing: Who is Judge Amy Coney Barrett?

Now Playing: Missouri governor tests positive for COVID-19

Now Playing: VP Pence discusses 200,000 COVID-19 death milestone, Supreme Court and race relations

Now Playing: Vice President Pence defends massive campaign rallies: 'We're in an election year'

Now Playing: Hundreds gather to remember Ruth Bader Ginsburg, 1st woman to lie in repose

Now Playing: Cindy McCain formally endorses Joe Biden