We might expect that public opinion would celebrate the end of dictatorship and the transfer of power to the people. But the normal trajectory of public opinion at a time of political change is a burst of intense excitement, hope and euphoria as the change takes place followed afterwards by a combination of exhaustion, disillusionment and apathy. American Presidents seldom fulfill the hopes and expectations generated during their successful election campaigns. Even if they are judged favourably by history, they are likely to disappoint their contemporaries. Once newly elected governments have had time to make their own mistakes, or even become associated with contemporary disasters that are not of their own making, nostalgia for predecessors is likely to grow. This cycle of public opinion is one of the fundamental dynamics of democracy that balances the government's power of propaganda and encourages alternation in office. (emphasis mine)
This "fundamental dynamic" explains a lot. Why does the party of the incumbent president lose during subsequent elections? Why does support for wars spike when it's finally declared, then decay? How can people cheer every four years at political conventions, instead of rolling their eyes?
This opinion cycle also helps explain why I'm so alienated from modern political culture. I'm a flat-line political cynic. My expectations start very low, and I'm rarely surprised. The main thing that still surprises me - no matter how many times I remind myself that voters aren't rational - is that everyone else doesn't think the same way.