How has the role of the presidency and the federal government changed since 1980?

Both the presidency and the federal government have changed greatly since 1980.
Ronald Reagan became president in 1980. The institution of the presidency had been weakened by the unsuccessful Vietnam War and the resignation of Richard Nixon after the Watergate scandal. Reagan sought to strengthen the office and project strong leadership both at home and abroad. Reagan was the oldest man ever to become president, but he exuded charm and vitality. Reagan's successors have, to a greater or lesser degree, tried to maintain an image of vigor. One part of this has been the maintenance of a large and expensive military force.
Reagan's economic policies, known as Reaganomics, have continued to influence the United States. Reagan sought to stimulate economic growth by cutting taxes and reducing regulation. Despite the fact that his tax cuts favored the rich, caused the national debt tp triple (ironically, as the Republican party's platform is reducing spending), and ultimately lowered the quality of life for working-class people, Reagan's economic ideas persist within the Republican Party to this day. Many presidents since Reagan have generally continued these policies, and as a result, the tax system is much less progressive than it used to be and the national debt has steadily climbed.
Another result of the Reagan era has been an increase in public distrust of the national government. "Government is not the solution to our problem; government is the problem," Reagan said. Many Americans do not believe the government should be involved in healthcare, education, or other aspects of their daily lives. This has widened the divide between the two major political parties, with Democrats generally wanting to expand government programs and Republican generally wanting to restrict them.
The rise of the internet has had a major impact on the national government. Its political ramifications were not foreseen and its impact has been both positive and negative, as has been evident in the most recent elections.
American elections have become more problematic for other reasons as well. One problem that has become obvious over recent decades is the Electoral College. Because of the Electoral College, candidates are able to take office after winning fewer popular votes than their opponent. As for Congressional elections, gerrymandering has worsened in recent decades.