Republicanism is not easy to summarize. Republicans themselves are loath to be pigeonholed. In recent years they have been loath to be identified. During the '70s, while other minorities were coming out of the closet, Republicans have been going in. If you ask a man what party he belongs to and he mumbles something you can't understand, you don't have to ask him to speak up. He's Republican, all right.

It didn't start with Watergate. It started shortly after Abraham Lincoln, the first Republican president. Things began to go awry when Lincoln took a break from the Civil War to go to the theater.

Lincoln was succeeded by Andrew Johnson, the first Republican president to be impeached. Johnson was succeeded by Ulsses Grant, the first Republican president to be our worst president, the second being Warren Harding. Harding was succeeded by Calvin Coolidge, who got out while the getting was good, thereby setting an unheeded example for later Republicans, notably Herbert Hoover, his successor, the first Republican president to be regarded by most Americans as even worse, if possible, than Harding.

The next Republican president was Dwight D. Eisenhower, who took the precaution of not becoming a Republican until he was ready to become president. Though not a truly disastrous president himself, Eisenhower laid the foundation for a full restoration of the Republican tradition by selecting as his vice president a promising young man named Richard Nixon.

In 1960 Nixon lost the presidency to John Kennedy when early returns from California and late, nay, posthumous returns from Illinois showed Kennedy ahead. It was shortly after that election that Nixon made his finest presidential decision, namely a decision not to become president. A crack reporter and friend of Nixon's named Earl Mazo had prepared a huge expose showing that Kennedy's Illinois victory had been due to what might be called the purgatory vote. The story might have upset the election and would certainly have upset Camelot, but Nixon ordered is squelched. The result was ultimately the great Society, Vietnam and a string of Kennedys longer than Banquo's line.

Nixon was far from finished. In 1968, with the nation still reeling from his decision not to become president, he decided to become president. He never quite achieved his goal of bringing the country together. pThe nearest approach to that came in 1972, when the Democratic nominee, George McGovern, united the nation in the conviction that even Nixon was preferable.

Critics -- and there were many -- charged that Nixon himself had no convictions. He did come close, however, and several of his aides were to earn convictions during what began as his second term. Those events are too intricate to be recounted here. But it appears that after his gallant act of 1960, Nixon and a few subordinates of the overzealous persuasion felt that they had at least a minor burglary coming in return. Nixon became the third Republican president to be our worst president, nearly the second to be impeached and the first to resign from office.

The Democrats, ever ungrateful, begrudged him even his pardon by Gerald Ford, his successor, who as vice president had succeeded Spiro Agnew, the first Republican vice president to be our worst vice president, and so forth. In 1976 Ford became the only man ever to be outwitted by Jimmy Carter.

Historians trace the political decline of the Republican Party from 1929, when many of its rank and file leaped from the upper stories of Wall Street skyscrapers. Fifty years later, however, the party is on the road to recovery. Its probable nominee for 1980, Ronald Reagan, was unable to buy television time to announce his candidacy; but if he is elected, his old movies and his speeches will doubtless command prime time, and he will become the first president to preempt himself.

Naturally a short survey like this one can't cover everything. We have made no mention of such luminaries as Sen. Joseph McCarthy, who hoped to depopulate the State Department, and Barry Goldwater, who hoped to defoliate Southeast Asia; nor of such prophets of Republicanism as Kevin Phillips, who as early as 1970 foresaw an "emerging Republican majority." Suffice it to say that nine years later, Phillips is still ahead of his time.