Now Playing: Trump enters talks with Moon amid uncertainty over North Korea summit

Now Playing: Georgia voters turn out for primary elections

Now Playing: Trump meets South Korean leader, 'demands' DOJ investigates FBI

Now Playing: Trump says North Korea summit 'may not work out'

Now Playing: Rubio says administration short-sighted with Chinese telecom negotiations

Now Playing: Primaries in Southern states shed light on midterms

Now Playing: DHS secretary 'not aware' Putin tried to help Trump win 2016 election

Now Playing: Trump raises doubts North Korea summit will happen in June

Now Playing: 'A lot of people are saying they had spies in my campaign': Trump

Now Playing: Democrats slam Trump's call for new DOJ probe

Now Playing: Hillary Clinton pokes fun at Trump, herself in Yale speech

Now Playing: Former President Carter ribs Trump's 'crowd size' during graduation speech

Now Playing: Pompeo outlines demands for a new treaty with Iran

Now Playing: New CIA Director Gina Haspel sworn in

Now Playing: Trump responds to Texas school shooting

Now Playing: Jared Kushner hosts first forum on prison reform at White House

Now Playing: WH: School safety commission 'activated' in wake of Texas school shooting

Now Playing: Embattled Missouri Gov. Eric Greitens bracing for impeachment proceedings

Now Playing: Farm bill fails in the House 198-213

Now Playing: Trump names Robert Wilkie as new VA secretary nominee