Final answer:
From 1968 to present, U.S. politics have experienced rising partisan polarization with a notable decline in bipartisan cooperation, a growing ideological divide, and a continuing dominance of the two-party system.
Step-by-step explanation:
The late 1960s marked the beginning of a shift in U.S. political party dynamics. Initial decades, such as the 1960s and 1970s, were characterized by a relatively high degree of bipartisan cooperation and legislation passing with support from members of both parties, many of whom had moderate voting records. However, from the 1980s onwards, both the Democratic and Republican parties began to polarize significantly in Congress. Moderate members became rarer as more ideologically driven candidates were elected, leading to Democrats becoming more liberal and Republicans more conservative. This shift resulted in less cross-party collaboration, with the opposition party increasingly willing to challenge presidential initiatives, a stark change from previous norms of public support for the president especially in foreign policy.
By the 1990s, the era of bipartisanship had largely ended, leading to bitter inter-party competition. Despite the negative aspects of this trend, it provides clear distinctions between party platforms for voters and ensures competitive elections, which are signs of a healthy democracy. The implications of polarization include fewer elected moderate officials and greater ideological distance between the parties. This has led to more consistency in congressional voting along party lines and a reduction in moderate voter participation in primaries, with some becoming independents or only voting in general elections.
Throughout this period, U.S. political parties continued to evolve, mirroring broader societal changes, and maintaining a predominately two-party system due to electoral rules like plurality voting. Though minor parties occasionally surfaced, the major parties have consistently adapted their coalitions to stay in power, aligning with social, demographic, and geographic divisions in the country.