BERLIN - Here in Berlin five years ago, Barack Obama addressed one of the largest and most enthusiastic crowds he's ever seen. He was treated as such superstar that the McCain campaign responded with a TV commercial using footage of the Berlin speech to brand Obama as a celebrity, not a leader, comparing him with Paris Hilton and Britney Spears.

This time around the longest lines here at the Brandenburg Gate are those for water - it's hot, almost 90 degrees. Where 200,000 came out to see Obama speak in 2008, today's audience will be just 4,000 - invitations doled out by the German government to students and various political figures.

Obama is a still a relatively popular figure here, but he now finds himself under fire over some of the very policies that made President Bush so unpopular with the Europeans. At a press conference this morning, he faced tough questions about the Guantanamo Bay prison (still open), US drone strikes and NSA spying. At one point, Obama felt the need to reassure the Germans that no US drone operations are conducted from German territory.

One bright spot for Obama: He will be giving the speech from where he wanted to speak in 2008: the east side of the historic Brandenburg Gate. In 2008, he was denied the right to speak here by German Chancellor Angela Merkel because she didn't not want this sacred site exploited for political purposes. This year, Merkel - now facing her own reelection campaign - will join Obama here, speaking just before he does.

Today President Obama will invoke two of the most memorable presidential speeches in modern history - Kennedy's 1963 "Ich bin ein Berliner" speech and Reagan's 1987 "Tear down this wall" speech - both delivered here.

The idea, White House officials say, is to tap into the energy and legacy of those great Cold War moments, calling for the kind of effort that won the Cold War to be made to confront today's major challenges - especially climate change and nuclear proliferation.

On nuclear proliferation, Obama will call for reducing US and Russian nuclear stockpiles in Europe by 30 percent. That would be significant - but he needs to get the Russians to agree.