ABC News’ George Stephanopoulos reports: Democratic presidential candidate Barack Obama holds a 50-46 percent lead over Republican presidential candidate John McCain among likely voters, according to the latest ABC News/Washington Post poll. However independent and undecided voters, who could make all the difference in a tight election, are shifting back and forth between Obama and McCain. After the Republican convention, McCain was up by about 10 points among independent likely voters, according to an ABC/Post poll released earlier this month. Then, last week Obama has a big swing and was up by 14 percentage points, but in our latest poll, McCain has pulled ahead by three percentage points. We’ve seen similar dramatic moves among white women, another group whose preferences are changing with each new poll. After the Republican convention, McCain has a double-digit lead among white women, with many pundits crediting his new vice presidential pick Alaska Gov. Sarah Palin for the shift in voter preferences. Last week Obama pulled ahead by two percentage points with white women, but the ABC/Post poll released today finds McCain regaining sizeable 11 percentage point lead over Obama with this group. One in five voters say they could still change their mind in this election. (Bradley Effect) It is those undecided voters and white women voters who will hold the key to who wins the White House in five weeks. The poll also found that President Bush is far and away the biggest drag on McCain right now. He has a new disapproval rating of 70 percent, which is a record for all presidents going back to the beginning of public opinion polling in 1938. The problem for McCain is that a majority of Americans – 53 percent – believe he would take the country in the same direction as Bush. When it comes to the all-important Commander-in-Chief test, a majority of Americans still do not believe Obama would be a good Commander-in-Chief. The poll found McCain leading Obama 73-46 percent on who would make a good Commander-in-Chief of the military. But for the first time, the poll found a majority of Americans – 52 percent – who say Obama has the experience to serve effectively as president.