Final answer:
Americans' party identification trends over time are characterized by frequent fluctuations, with a growing number of independents who often lean towards a major party. Additionally, there has been increased polarization and periods of party realignment, reflecting changes in voter affiliations and preferences.
Step-by-step explanation:
The trends in Americans' party identification over time can best be characterized as B) Fluctuating frequently. Gallup polls suggest that while a majority of American adults identify as "Republican" or "Democrat," a significant proportion of the population identifies as independent, though many of these independents lean towards one of the two major parties. Over time, there have been shifts in party affiliations, with the number of self-identified independents growing and the proportion of people identifying as Republican decreasing slightly. These trends reflect a changing political landscape in which increases in polarization and the alignment of political parties have occurred, especially since the 1990s. During elections, however, most voters still choose one of the two major parties. Periods of party realignment have also witnessed shifts in voter affiliations, responding to demographic changes and shifts in voter preferences.
Overall, party identification among Americans has seen some stable patterns but also significant fluctuations, particularly among those who identify as independents, indicating a dynamic and evolving party system rather than a static one.