On Friday, America will mark the 50th anniversary of the Watergate break-in. The scandal that riveted the nation and forced the resignation of a president is taught in schools as a dark chapter in history. It is more than that, however. Its legacies have shaped the conduct of politics and public attitudes toward government ever since.

Watergate, along with the Vietnam War, marked a dividing line between old and new, ushering in a changed landscape for politics and public life — from a period in which Americans trusted their government to a period in which that trust was broken and never truly restored. “It’s a hugely important historic moment,” said Julian Zelizer, a historian and professor at Princeton University. “And we entered a new era when it was over.”

Though not a straight line by any means, the links between former president Richard M. Nixon and former president Donald Trump also are clearly identifiable, from their ruthlessness to the win-at-any-cost calculus of their politics. That their presidencies played out differently — Nixon resigned amid impeachment proceedings; Trump served his entire term and may seek another despite twice being impeached, although not convicted — is testament to a more deeply polarized electorate, the erosion in the strength of democratic institutions and the transformation and radicalization of the Republican Party.

The aftermath of the Watergate scandal opened up the operations of Congress but also contributed to making the legislative body less manageable. The scandal helped change the way reporters and government officials interacted with one another. A more adversarial relationship has existed ever since. The era spawned reforms that worked and some that did not, from campaign finance to intelligence.

Politically, both major parties were affected. A seemingly broken Republican Party reconstituted itself with a more anti-government ideology. Democrats, led by the big class of 1974, slowly began a transformation away from the lunch-pail coalition of White working-class voters and toward a more diverse coalition that now includes highly educated coastal elites.

Not everything that has happened since Watergate is directly attributable to the scandal itself. Some changes in society and politics were already beginning to be felt before burglars were arrested early on the morning of June 17, 1972, after breaking into the Democratic National Committee headquarters at the Watergate building. But subsequent investigations; the indictments and convictions of Nixon administration officials; the impeachment articles passed in the House Judiciary Committee; and Nixon’s resignation combined into an event that shattered the confidence and idealism of previous decades.

Garrett M. Graff, author of the book “Watergate: A New History,” describes Watergate as a dividing line in history — the event that moved Washington from a sleepy capital dominated by segregationists, veterans of World War I and print newspaper deadlines to a capital ruled by a new breed of politicians, a more adversarial media now in the digital age and a country deeply skeptical of government and politicians.

“The Vietnam War, the Pentagon Papers and Watergate … fundamentally rewrote the relationship between the American people and their government,” Graff said, “and caused a collapse in the public’s faith in those institutions that our nation’s leaders are still struggling with today.”