It is a little bit difficult to make judgments about political culture so soon after the fact. Things that appear to be changes in political culture may be very transient and will no longer seem important when we look back at this time from the future. That said, it appears that there have been two important changes in political culture since 2004.
First, political culture seems to have gotten much more confrontational and angry in these years. This might have started with George W. Bush and the mutual hatred that seemed to exist between him and liberals. It appears to have continued to the present. This may simply be due to us having two divisive presidents in a row, but it may also be due to such factors as the ubiquity of social media and of partisan media outlets. At any rate, the possibility for bipartisan cooperation and understanding seems to be much lower than it was before 2004.
Second, there is a much more populist tone to political culture. This appears to have arisen with the “Tea Party” and the financial crisis of 2008. This has been seen mainly on the right. However, there is also left-populism with anger at big business. This was manifested in the “Occupy” movement.
Thus, there seem to have been at least two major changes in political culture since 2004.
Thank you so much pohnpei397, that helped a lot!