However, I believe we have already witnessed at least four important moments along the way. Following are the
1). July 2 -- Campaign Shake-up -- McCain loyalist Rick Davis is demoted and Steve Schmidt takes control of the "day-to-day operations" of the McCain campaign. As a result, McCain begins to develop a consistent message and to paint Obama as "out-of-touch."
2.) July 17-25 -- Obama's Audacious Trip -- Obama prepares for an international trip which will be covered by media stars. It is observed his plane has the 'President' label on it. After touring the Middle East, Obama gives a speech in Berlin, where he talks about America's imperfection. On his way to Paris, it is revealed that Obama skipped a meeting with injured U.S. troops. Each of these events helps underscore McCain's message about Obama.
3.) July 30 -- Celebrity Ad -- McCain unveils "Celebrity ad," which features Paris Hilton and Britney Spears. The ad is mocked by some, but reinforces Obama's image as a "celebrity." It also garners a ton of free media attention.
4.) August 8, 2008 -- Georgia -- Russian tanks enter Georgia's breakaway provice of South Ossetia. McCain quickly condemned Russia, while Obama was "characteristically circumspect."
5). August 16 -- Saddleback -- After Obama returns from vacation, McCain and Obama appear at a forum with Pastor Rick Warren at his Saddleback Church. McCain appears relaxed and in control, while Obama criticizes Justice Clarence Thomas and says abortion is "above his pay grade."
In this business, there is a tendency to focus solely on what is happening today. This allows little time for analysis of past events. But it is only through introspection that we can step back and get a big-picture view -- and assess what is working (or not working) over time. Clearly, McCain's momentum began with a staff change which resulted in developing and driving a consistent message about Barack Obama.
Update: Due to popular demand, I've added Russia's invasion of Georgia as number 4...