U.S. Democratic presidential candidate Barack Obama wrapped up his three-day European tour Saturday after meeting leaders of major U.S. allies and harvesting enormous popularity among the public of the three countries he has traveled to.

His high-profile visit to Germany, France and Britain was viewed by observers here as an attempt to sharpen his diplomatic edge and boost election campaign against rival Republican presidential candidate John McCain.

It was imperative for Obama to travel abroad to convince swing voters at home that he has the ability to lead his country and its European allies.

As some U.S. voters have doubted the ability of Obama, who is much younger than McCain and lacks experiences in diplomacy and many other fields, to lead the United States if he is elected president.

Obama is only a one-term senator, while his rival McCain, a veteran of the Vietnam war, has been a lawmaker for 26 years.

Furthermore, McCain paid a series of visits to the Middle East, Canada, Mexico, Colombia and Europe to polish his diplomatic credential.

It seemed that Obama got what he wanted from his visit to Afghanistan, Iraq and the Middle East--"a deepening of a set of concerns" he already had.

He said that there was nothing that "I saw that caused me to change my basic strategic assessment" on security and foreign policy.

Obama chose Germany, France and Britain as his testing battlefield for diplomacy out of the consideration that the three countries have been the most important traditional U.S. allies in Europe.

Discussing Afghanistan, Iraq, the Iranian nuclear crisis and climate change with German Chancellor Angela Merkel, French President Nicholas Sarkozy and British Prime Minister Gordon Brown, Obama wanted to showcase to domestic voters that he could stand gracefully side by side with such political figures if elected.