This is the campaign that is defying expectations. In fact this is the campaign where expectations died.

This was supposed to be a short nomination fight in both parties. The Democratic struggle was supposed to be brief and bloodless; former Secretary of State Hillary Rodham Clinton was supposed to be the indestructible, indefatigable and inevitable candidate. The Republican struggle was supposed to be short and sweet; the party elders rigged the GOP rules so the contest would be over before the snow melted.

This was supposed to be a contest of titanic political families, a sobering challenge to the American idea that here we abjure dynasties. The expectation was that two legatees of political tribes that have been clashing since 1992, the Clintons and the Bushes, were headed for a final smack-down in November.

This was supposed to be a campaign where demographics were destiny, where the Republicans would pay for their difficulties attracting minority voters, especially Hispanics, and where the Democrats would reap the benefits of the Obama boom among young people.

Then again, Gov. George Romney was supposed to be a formidable Republican candidate in 1964, just as Sen. Edmund Muskie was supposed to be the certain Democratic nominee in 1972. And then again, hardly anyone suspected that Sen. Gary Hart rather than Sen. John Glenn would be the ultimate rival to former Vice President Walter Mondale in 1984, just as the smart money was on an early withdrawal of Sen. John McCain in 2008.

Why we set up these false premises is a subject for another day probably, like the song from “Annie,” a tomorrow that is always a day away. So for the time being let’s be content to clear away the cobwebs and the sorrow, and find lessons in the expectations that haven’t been fulfilled this campaign.

Just last week, the Clinton camp conceded that the swift campaign it had expected may become a longer slog. Some of that talk, and the speculation about a $50 million ground campaign that limped along until April, was an expectations game of its own.

The Democrats (here comes a phrase this typist never thought would emerge from his fingers) are more disciplined than the Republicans and (in another shocking break from expectations) the Democrats have more centralized, top-down control. Their nomination rules provide a major role for party leaders, who are not warm to Sen. Bernie Sanders, a 74-year-old socialist from a state with three electoral votes. Moreover, they’re not the Labour Party, and party leaders are not eager to put forward the American equivalent of Michael Foot, whose 1983 statement of British socialist principles was described as the longest suicide note in history.

So, while it is not unlikely that Mr. Sanders of Vermont could win next month’s early tests in Iowa and New Hampshire, there is little likelihood of his prevailing in later contests. The Clinton campaign would be wounded with two such consecutive defeats but it would not be ended. When the Clinton camp talks of a long campaign, it is speaking of disappointment, not danger. It is resetting expectations in a way that will preserve its dignity and its prospects.

As for the Republicans, the planning for a brief campaign is in shambles, unless it turns out that the campaign is a Hobbesean nightmare that is nasty, brutal, short and ends with the nomination of businessman Donald Trump or even Sen. Ted Cruz of Texas, who was not whom GOP grandees had in mind for their nominee, though do not forget that party chairman Reince Priebus has deep Tea Party roots.

It now seems that the nation examining the endurance of political legacy is Canada, which just elected the son of longtime Prime Minister Pierre Elliott Trudeau to its top office, and not the United States, where the prospects of a Clinton-Bush rematch are dimming, though not extinguished. Now the nomination of former Gov. Jeb Bush of Florida would be regarded as an upset, not the fulfillment of expectations; the latest Wall Street Journal/NBC News poll indicated that Mr. Bush is viewed unfavorably by 46 percent of voters.

One more: No longer are Democrats crowing about their demographic destiny, a theory holding that the party’s longtime success with minorities and its astonishing Obama-era appeal to young people would provide it with a powerful advantage through the first quarter of the 21st century.

Young people are wary of Ms. Clinton, who remains likely to win the party’s nomination, and attracted to Mr. Sanders, who is not likely to do so and whose supporters, with their youthful enthusiasm and their lack of experience with political disappointment, may become alienated. Among New Hampshire voters up to age 50, according to a Monmouth University poll, Mr. Sanders holds a 58-30 advantage over Ms. Clinton. Moreover, the skepticism young women have for Ms. Clinton is a surprising new vulnerability the Democrats are only now beginning to confront.

The prospect that one of the Cuban-Americans, Mr. Cruz or Sen. Marco Rubio of Florida, might be on the Republican ticket could be an antidote to the party’s Hispanic challenge, which is only growing larger as Mr. Trump continues to push for a wall along the Mexican border. Last week’s Journal/NBC News Poll indicated that 45 percent of Latinos view the party more negatively as a result of this campaign, which has been dominated by Mr. Trump.

Former Gov. Mitt Romney of Massachusetts, the 2012 Republican nominee, captured only 27 percent of the Hispanic vote, down from the 40 percent carried by George W. Bush in 2004, prompting GOP leaders to worry about the party’s prospects in such electoral-college battlegrounds as Colorado, Nevada and Florida, Mr. Rubio’s home state, this autumn. Some Republican strategists even worried that Texas, which has voted Republican in every presidential election since 1980, could trend Democratic by the end of this decade. Mr. Cruz’s presence on the GOP ticket would end those concerns and seal Texas and its 38 electoral votes in the Republican column.

“The Hispanic vote is more up for grabs than people realize,” said Donald T. Critchlow of Arizona State University, whose new book, “Future Right: Forging a New Republican Majority,” is to be published this spring. “That’s especially so when you look at the issues that concern them. They share the values of the rest of the country and are not necessarily Democrats.’’ Another expectation being re-examined.