in the stands of lineups of big hitters, dave winfield, derek jeter, plus key players on the national security roster, a starkly different setting this morning at the u.s. ambassador's residence, a secure call to belgium's prime minister. >> this is yet another reminder that the world must unite. >> reporter: and this from the first lady. >> we are outraged and heartbroken over the horrific attacks today in belgium. >> reporter: tonight raul castro saw the obamas off at the airport, the president sticking to his scheduled next stop, a state visit in argentina. andrea mitchell, nbc news, havana. >> reporter: i'm hallie jackson, the images from brussels, like paris and san bernardino before, now bringing into focus the dramatic differences between the party's front-runners. >> i would close up until we figure out what is going on. >> i think there are a lot of things we have to do to intensify our efforts. i think closing our borders is not one of them. >> reporter: for hillary clinton, a chance to prove her national security credentials. for donald trump an opportunity to seem more pre