America has not moved left.
According to CNN's 2008 exit polls, 34 percent of voters identify themselves as conservative, 44 percent as moderate, and 22 percent as liberal.
In 2004, the respective numbers were 34, 45, and 21 percent.
In 2000, the numbers were 29, 50, 20.
Do I need to draw a graph?
Obama rode an economic collapse and a non-conservative Republican candidate into office. Mostly sheer luck, as the Democrats would have failed miserably with their original plan of riding Iraq into office.
I suggest Democrats don't fall into the same trap the Republicans did after 1994. You haven't converted this country into Sweden just yet.