Generate a short summary this sentence:
us president barack obama will visit dresden and the former nazi camp buchenwald this week during the german leg of a tour underlining the importance of fighting extremism , past and present .

Summary:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
spectre of extremism to drive obama 's german visit