Now Playing: Senators react to Supreme Court ruling in favor of travel ban

Now Playing: Trump amps up feud with Democrat Maxine Waters

Now Playing: Trump escalates feud with California Democrat Maxine Waters

Now Playing: Terry Crews testifies about sexual assault on Capitol Hill

Now Playing: Supreme Court rules in favor of Trump's controversial travel ban

Now Playing: Partisan divide grows sharper in US, but Bush-Clinton friendship endures

Now Playing: Trump attacks late-night comedians during campaign rally

Now Playing: Former US presidents get together for a sock-sational photo

Now Playing: Trump calls Democratic lawmaker 'extraordinarily low IQ person'

Now Playing: Sessions defends administration's border defense tactics

Now Playing: The Briefing Room: WH press secretary takes questions on immigration

Now Playing: Congresswoman urges Americans to confront Trump administration officials

Now Playing: Trump blasts Jimmy Fallon, tells him to 'be a man'

Now Playing: This Week Off the Set with Chris Christie, Donna Brazile

Now Playing: Immigration may 'stoke up' GOP, but is a 'losing issue' in Nov: Matthew Dowd

Now Playing: President Trump continues to blame Democrats for lack of immigration reform

Now Playing: Immigration policy failure a 'political' and 'moral' crisis: Donna Brazile

Now Playing: Trump takes on immigration at campaign-style rally

Now Playing: Former top Trump aide Tom Bossert on border security, family separation

Now Playing: Sen. Jeff Flake: Trump has 'consolidated his hold on the Republican Party'