Almost every American of a certain age remembers where he was when President John F. Kennedy was assassinated on Nov. 22, 1963.

The nation stopped and mourned. In their grief, few Americans wondered how the tragedy would affect domestic politics, and in the short run relatively little changed. “Let us continue,” President Lyndon Johnson said when he addressed Congress after the funeral.

In the longer run, the effect on partisan politics, on the people and press and parties, was profound. And those effects continue to reverberate today.

Unlike Lincoln and Roosevelt, who were taken from the stage just as they completed historic undertakings -- the Civil War, World War II -- Kennedy was murdered when he and his administration were in the middle of things. The tax cuts he had proposed in February 1963 and the civil rights bill he had endorsed that year had been long delayed in Congress. But, contrary to the conventional wisdom of the time, they were well on their way to passage when he died.

Relations with the Soviet Union were stable after resolution of the Cuban Missile Crisis in October 1962. The United States was already sending more troops to Vietnam, and Kennedy’s approval of the Nov. 1 coup against the Diem government committed the United States to continuing responsibility there.

Politically, Kennedy’s job approval had declined significantly from about 70 percent, but only because of the defection of Southern whites on civil rights. In the rest of the nation he was highly popular and running ahead of any Republican by margins larger than those enjoyed by Franklin Roosevelt. That suggests that he would have nearly matched the 61 percent of the vote Lyndon Johnson got in November 1964, with some slippage in Johnson’s Texas and the Border South.

Lee Harvey Oswald is led down a corridor of the Dallas police station for another round of questioning. (AP Photo)

The assassin, Lee Harvey Oswald, was a communist who had lived for three years in Soviet Russia and married a Russian woman; he later tried to travel to Cuba and joined a pro-Castro group. But Oswald was murdered while being moved from prison two days after Kennedy's death and any chance to learn more from him was lost.

That helped to spawn conspiracy theories that have thrived ever since, even though the commission appointed by Johnson and headed by Chief Justice Earl Warren named him as the sole assassin. Americans did seem to accept one corollary of that conclusion, that the Soviet or Cuban governments were not involved, which would have amounted to an act of war.

Instead of turning against communists, many American leaders turned against America, and this had a transformative effect on American politics. New York Times columnist James Reston, the dean of American journalism, said Kennedy’s assassination was a symptom of a sick society. The distinguished historian Arthur Schlesinger Jr., an aide in the Kennedy White House, said that Kennedy’s death was evidence that America was an overly violent society. Their views were in line with many people’s first assumption when they heard the president had been killed in Dallas — that a rabid right-winger killed him.

The Democratic lurch to the Left was symbolized by the nomination in 1972 of George McGovern, who urged 'Come home America!' in his acceptance speech — the opposite of the Kennedy inaugural's 'bear any burden, pay any price.'

The city was known then for its loud-mouthed conservatives who, among other things, jostled Lyndon and Lady Bird Johnson in a downtown hotel in 1960. But none of that fit the facts that quickly emerged. Oswald was an exceedingly atypical American, violent crime rates were far below the level they would reach in a few years, and Kennedy had been a lukewarm supporter of civil rights until persuaded by events in June 1963 that he must take a stand.

Among Americans generally, there was a loss of confidence in the nation and its institutions. In the two decades before the Kennedy assassinations, pollsters generally found great confidence in presidents and major institutions, the prime exception being when the Korean War became stalemated in 1951. This was not unreasonable: The United States had won World War II and, unexpectedly, the nation experienced an economic boom in the postwar years.

Americans in the years after 1963 were more inclined to become disillusioned with their leaders, and the next two presidents were in effect forced out of office, Johnson by Vietnam and Richard Nixon by Watergate. The press reported setbacks and abuses in Vietnam, and portrayed the defeat of the Communist Tet offensive as a victory. The Kennedy assassination resulted in a more liberal Democratic Party.

In life, Kennedy was a cautious politician, cool and calculating, hesitant about championing civil rights, placing a higher priority on tax cuts than domestic spending increases. He was a vigorous Cold Warrior, sharply increasing defense spending and sending more troops to Vietnam. Kennedy was depicted in political oratory and popular culture as a comrade of Martin Luther King, despite his conspicuous absence from Washington on the weekend of the great march in August 1963. It was widely argued that Kennedy would never have escalated the Vietnam War as Johnson did, but there was little evidence of that except for an ambiguous phrase Kennedy uttered in an interview with CBS News anchorman Walter Cronkite.

Astronaut John Glenn and President John Kennedy inspect the Friendship 7, the Mercury capsule which Glenn rode in orbit. (AP Photo)

Democrats after Kennedy became fixated on alleviating poverty in America, but Kennedy’s grand project was to put an American on the moon. Robert Kennedy, the friend and defender of Joe McCarthy in the 1950s, became a liberal senator, though one who sensibly sought to learn whether antipoverty programs were getting any results. Edward Kennedy, elected to the Senate in 1962, endured jibes that his only qualification was his name, but in time he became the lion of the Democratic Left.

The Democratic Party’s lurch to the left was symbolized by the nomination in 1972 of George McGovern, who urged “Come home America!” in his acceptance speech — the opposite of the Kennedy inaugural’s “bear any burden, pay any price.” Democrats, the more hawkish of the two parties in the half-century from 1917 to 1967, became the more dovish party in the half-century since. Many Democratic candidates opposed the death penalty — an unthinkable position for Kennedy. And, of course, Kennedy had never taken liberal positions on abortion, drugs or homosexuality; in his time those were not political issues but crimes.

For all this Democrats paid a political price, winning the presidency only once in the quarter-century after Kennedy’s death. Republicans, with some lurches, became the more conservative party and in a time when liberal policies seemed not to be working at home or abroad that was a winning strategy, at least at the presidential level.

Edward Kennedy, running as a liberal alternative to Jimmy Carter, was decisively beaten in the Democratic primaries, and then Carter was the landslide loser to Ronald Reagan. Bill Clinton, who in July 1963 as a Boys' Nation delegate shook Kennedy's hand at the White House, broke the string by forging a New Democratic politics and won the presidency twice. Barack Obama combined a more leftward agenda with the potential to be a first -- the first black president, as Kennedy was the first Catholic one. But in eight of the 10 elections after Clinton's victory in 1992, Republicans have won majorities in the House of Representatives. Most Americans have Republican governors and Republicans are in their strongest position in state legislatures since the 1920s.

The news media have continued in the same adversarial role toward political leaders, especially but not always toward Republicans. The example of Bob Woodward and Carl Bernstein exposing the Watergate scandal has remained the beau ideal of journalists. At the same time, the structure of journalism has changed. Kennedy's death came when Time and Newsweek were influential national voices and just after CBS and NBC introduced the 30-minute nightly newscast (ABC followed in 1968). For three decades these newscasts' anchors and producers, informed always by the New York Times and Washington Post, effectively determined what most Americans knew about politics and government.

Jackie Kennedy and her children, Caroline and John, Jr., at St. Matthew's Cathedral behind the late President's casket. (AP Photo)

The rise of cable television and new cable news networks ended this dominance and offered a cacophony of voices, many of them partisan, from which viewers can choose. In the past dozen years the Internet has destroyed the business model of metropolitan newspapers and weekly news magazines and caused many to disappear or migrate to the Web.

Americans’ trust in institutions and leaders has occasionally returned toward the heights it reached in the two decades before Kennedy’s death, primarily in periods of apparent peace and prosperity during the Reagan and Clinton presidencies. But the default mode seems to be distrust. To an unnerving extent, America is still living in the wake of the murder of John F. Kennedy.