From a 2000 speech by William Mayer of Northeastern University, link [emphasis added]:
... the work of the McGovern-Fraser Commission also had an important effect on the operations of the Republican Party. This came about partly because the Democratic party reformers helped promulgate new standards of openness and participation that the Republicans felt compelled to emulate, partly because when Democratic state legislatures changed their laws to correspond to the Democrats' new national rules, they usually applied the new provisions to the Republicans as well. Whatever the precise reasons, the Republican nomination process also changed quite dramatically during these years. As the number of presidential primaries increased, for example, it rose just as fast in the Republican party as in the Democratic.
... the nomination process was rocked by a second major set of changes. In 1974, in response to the Watergate scandals, Congress passed a law -- technically, a set of amendments to the Federal Election Campaign Act of 1971 -- that completely restructured the ways that candidates could raise and spend money while running for president. This law, with only a few modifications, is still in effect. It has lots of critics; but no one I know of denies that it is an important landmark in American electoral history.
The first election cycle to which both sets of rules applied was, of course, 1976. And though both parties had contested nomination races that year, it was the Democratic race that received most of the attention afterward and that did most to shape the view of the new nomination process that came to be held by practitioners, journalists, and scholars alike.
... the 1976 Carter campaign strategy became the prototype ... Almost every candidate since 1976 has felt compelled to emulate the four major premises of the Carter campaign: announce early, target Iowa and New Hampshire, do a lot of personal campaigning in those states, and then try to ride a wave of momentum to the nomination. As one Democratic strategist would comment in 1986, "Now there is only one strategy. It doesn't matter whether you are a Walter Mondale with deep ties to the party or whether you are a newcomer -- you both do the same things."
... the 1976 campaign had an enormous impact on the way that political commentators and political scientists viewed the presidential selection process. In the first place, it was the 1976 race that first established "momentum" as the great buzzword, the crucial concept, in understanding and interpreting a presidential nomination race. No election since then has run its course without a host of articles and reports speculating about which candidate has the momentum and how that may change in response to the most recent set of primary or caucus results.
... When Jimmy Carter ran for president in 1976, the schedule of primaries and caucuses started up quite slowly. It began, as I've already said, with the Iowa caucuses, which were held on January 19. The next major event didn't take place until five weeks later: that was the New Hampshire primary, on February 24. On each of the next four Tuesdays, there was a single primary. There was no primary on March 30, two on April 6, none on either April 13 or 20, and one on April 27. Not until May, in other words, did a large number of primaries take place on the same day. And the 1976 version of Super Tuesday, when California, New Jersey, and Ohio all held their primaries, didn't take place until June 8, the final week of the primary season.
Compare ... the Republican presidential candidates in 1996 ... primary and caucus season began in Iowa on February 12. This was followed, as in 1976, by the New Hampshire primary -- but where in 1976 five weeks had separated these two events, by 1996 Iowa and New Hampshire were just eight days apart. New Hampshire then was followed by: four primaries in the last week of February, nine primaries in the first week of March, eight primaries in the second week of March, and then four more primaries in the week after that. By the end of March, 1996, just five weeks after the New Hampshire primary, more than three-fourths of the delegates to the Republican National Convention had already been chosen. In 1976, by comparison, only 19 percent of the delegates to both parties' conventions had been selected by five weeks after New Hampshire.
That the 1976 calendar started up so gradually was one more way that the system helped encourage and sustain long-shot candidates. Simply put, it meant that a candidate like Carter did not have to campaign on a national scale until relatively late in the game. Candidates without significant resources of money, name recognition, and press attention could concentrate on a few early states like Iowa and New Hampshire, and assume that if they did well there, they would then have ample time to consolidate their advantage.
Today, by contrast, a presidential nomination race becomes, in effect, a national campaign from the very first day after the New Hampshire primary. Front-runners are, of course, much better prepared to make this kind of transition. Candidates like Ronald Reagan in 1980 and Walter Mondale in 1984 -- or Al Gore and George Bush this time around -- already have a national apparatus. The same cannot generally be said for people like Bill Bradley or John McCain.
... Of all the ways that front-loading changes the dynamics of a presidential campaign, perhaps the most important is its impact on fund-raising. Under the primary and caucus calendar that existed in 1976, candidates could -- and did -- expect to raise a lot of their money during the primary season. This, too, helped the non-front-running candidates. Long-shot contenders needed to raise only enough money to compete effectively in Iowa and New Hampshire. A good showing in those states would then bring in the money to contest the next few primaries, where a good showing would bring in yet more money, and so on.
A heavily front-loaded calendar, however, makes it considerably more difficult to finance a campaign this way. Under the federal laws passed in 1974, no individual can contribute more than one thousand dollars to a presidential candidate. This inevitably makes fund-raising a slow and labor-intensive process. The result, according to many observers, is that even if a long-shot candidate were to score a breakthrough win in Iowa or New Hampshire, he simply wouldn't be able to raise the money fast enough to compete in fifteen or twenty major primaries during the few weeks.
... What a good presidential selection process needs, in short, is some measure of flexibility: some capacity to question and test the front-runner, to ask if he really is the right person for the circumstances facing the party and the country, to make sure that he is not nominated just because he is the front-runner. And the more front-loaded the system becomes, the more I worry that it has lost this flexibility."