The chart shows that median household income in the two years after the most recent recession fell at a rate that nearly equaled its drop during the recession itself (the National Bureau of Economic Research judged that the most recent recession ended in June of 2009).
Much of the economic debate in the presidential race revolves around jobs, with Republicans pointing to disappointing monthly jobs reports and the nation’s unemployment rate, and Democrats noting the private sector job gains that have taken place under Obama's watch. But income is also a tangible metric for a lot of voters, and the static nature of the numbers is not encouraging for the president's case on the "are you better off" question.
This isn't the first time in history that median household income has continued to drop in the years following a recession. It happened after the recession at the beginning of the last two decades, as a second Pew chart shows:
But in both of those cases, the decline slowed from its rate during the recession. In the case of the most recent recession, it remained about the same in the aftermath.
All of this does not mean that it is impossible for Obama to make an overall case that the the country is better off financially than it was four years ago -- it just makes it harder. And he's already facing an uphill climb: the latest CNN/ORC International poll showed that a plurality of likely voters said they were worse off financially than they were four years ago.