Now Playing: Bannon: If GOP supports moderate immigration bill, Republicans could 'lose 50 seats'

Now Playing: Former WH Chief Strategist Bannon says Trump has never lied: 'Not to my knowledge'

Now Playing: Jonathan Karl: Trump may be 'uniquely positioned to get a deal with North Korea'

Now Playing: Chris Christie: 'If the president were to pardon himself, he would get impeached'

Now Playing: Former UN Amb. on revived NK summit: 'Danger now is this will be a gigantic photo op'

Now Playing: Giuliani: Mueller has 'high bar' to justify presidential subpoena

Now Playing: Top Senate Dem: Trump in 'high wire act without a safety net' on North Korea

Now Playing: Only two options on North Korea, 'peace or war': Sen. Lindsey Graham

Now Playing: North Korea expert: Trump and Kim both 'master disruptors' ahead of summit

Now Playing: As historic Singapore summit begins, some South Koreans have 'high hopes'

Now Playing: One-on-one with Sen. Marco Rubio

Now Playing: Sen. Marco Rubio: ‘North Korea will not denuclearize,’ Kim Jong Un’s efforts ‘all a show’

Now Playing: 'No evidence to support spy theory:' Top House Intel Committee Democrat

Now Playing: This Memorial Day weekend, honoring those who lost their lives in non-combat accidents

Now Playing: NFL 'caved' to Trump and fan base with new policy: Washington Post's Wesley Lowery

Now Playing: Former CIA director discusses next steps for North Korea summit

Now Playing: One-on-one with top Democrat on the House Intelligence Committee

Now Playing: Trump 'willing to throw almost anything against the wall:' Former CIA director

Now Playing: In Memoriam for April 2018

Now Playing: Parent who lost child to school shooting says focus needs to be on 'prevention'