Five years and 50 years. As President Barack Obama revisits Berlin, he can't escape those anniversaries and the inevitable comparisons to history and personal achievement. His 26-hour whirlwind visit to the German capital caps three days of international summitry for the president and marks his return to a place where he once summoned a throng of 200,000 to share his ambitious vision for American leadership. That was 2008, when Obama was running for president and those who supported him at home and abroad saw the young mixed-race American as a unifying and transformational figure who signified hope and change. Five...