berlin and a stretch of hallowed ground where american presidents have made history. Kennedy, reagan and candidate obama. Today he returned to talk climb change and nuclear arms. What a difference five years makes. Look, then and now. The crowd is much smaller today in part for security reasons. On this sweltering day and a challenging week for the president, the comparison was inescapable. Jonathan karl is in berlin tonight. Reporter: Battling a blazing sun and 90 degree heat, president obama spoke from where the berlin wall once stood. The heros that came before us now call to us to live up to those highest ideals. Reporter: Some of those heros were american presidents. I take pride in the word ice. Tear down this wall. Reporter: Today obama called for the same effort that was used in the cold car. The struggle for freedom and security and human dignity, that struggle goes on. Reporter: This trip was marked less by great speeches than by the challenges obama faces on the world stage. At the g 8 summit in ireland, body language spoke louder than words as obama clashed with putin over syria. And here in germany he faced tough questions about unfulfilled questions and controversies about the spine programs. This is not a situation in which we are rifling through the ordinary e-mails of german citizens or american citizens or french citizens or anybody else. Reporter: Second term presidents often find trips abrood as a way top find temporary escape from the problems at home. On this trip obama found that questions about how he is handling syria followed him every step of the way. Speaking of syria, one of the top issues on this