summit at the demilitarized zone dividing north and south korea. they went 20 steps into north korea. here's what the moment looked like. you will hear camera operators and security personnel throughout the video.

>> good to see you again. >> unexpected to meet you at this place.

>> get out of the way. >> move, move. >> come on. >> wait until they moved. rex thank you, mr. president. >> come on. >> where are they going?

they are going straight. >> doing great.

>> that made him the first u.s. president to visit our country. >> i believe this is an expression of his willingness to open a new future. >> i just want to say that this is my honor, i didn't really expect it, we were in the chip -- in japan for the g20. stepping across that line was a great honor. a lot of friendships have been made. this is in particular a great friendship, so i just wanted to thank you. that was very quick notice and i wanted to thank you.

[indiscernible] >> we are wrong to go inside and talk for a little while about different things. a lot of really positive things are happening. tremendous positivity. really great things are happening, in a lot of places. but we met, and we liked each other from day one. that was very important.

>> thank you, everybody. >> stayed behind me. behind me. >> move, move, move. come on. let's go.

[indiscernible] day, really, for the world, it's think about it. it's a great day for the world, and it's an honor for me to be here. >> come here.

it's ok. >> i have to say that when i became president of the united states, there was great conflict it iss area, and now great. >> yes, absolutely.

>> all of us together. >> hold it. stop. >> now, reaction to the president's visit to north korea, from democratic presidential candidate senator bernie sanders from vermont, amy klobuchar, and julian castro.