There are three words that should guide any interpretation of the 2024 election: Mind the gap.

Those three words define the problems and potentials of the major-party presidential election. They provide a way of measuring the course of the campaign. They explain the position the two candidates are in as they approach the final three weeks of struggle.

Here in brief form is the entire story of the election. Mind the gap:

— Between the air game and the ground game. The former are ads you see on television, particularly in the seven swing states, where it’s impossible to avoid a political appeal every seven minutes. The latter is what you don’t see and may not even feel: the efforts both campaigns are mounting to get their supporters to the polls and, in some nefarious cases, to keep their rivals’ supporters from voting or having their votes count — or matter. There’s some evidence that former President Donald Trump is being outspent in advertisements and is lagging in the ground game in the swing states. General rule of thumb: What you see on television isn’t necessarily what you will get on Election Day. Same goes, by the way, with lawn signs.

— Between voters who are undecided about whom to vote for and those who are undecided whether to vote. In some cases, they’re the same people; as unimaginable as it may be, there remain some few Americans who cannot decide between Vice President Kamala Harris and Trump. But there also are some people who are still weighing whether to vote at all; some of them find both candidates unacceptable and would rather not vote for either of them. In that case, Harris is probably at a disadvantage.

— Between what you feel and what is real. This syndrome is most pronounced among liberals who say they don’t know anyone who could possibly support Trump. Of course they don’t — that’s one reason why the country’s divisions are so stark. (There are some Trump supporters who could say the reverse, but probably not as many.)

— Between crowd size and vote size. For five years, dating at least to his 2017 inaugural, Trump has been obsessed with the size of his crowds. They matter in one sense, as a measure of the commitment and enthusiasm of his supporters. They also may matter as a means of mobilizing them to vote. But they do not matter as a measure of his popularity. The same can be said for the size of Harris’ crowds. Don’t forget: In both cases, these are spectator events — for Trump, a chance to view an unprecedented spectacle, and for Harris, a curiosity about a less well-known figure. Short aphorism: It is not the size of the crowd that matters, but the size of the vote. One doesn’t necessarily affect the other, as demonstrated by the huge crowds Walter Mondale attracted in 1984 … before losing 49 states.

— Between expectations and reality. Former Secretary of State Hillary Clinton could write a book about this gap. (In fact, she did: “What Happened,” 2017.) Forget the expectations. The ordinarily reliable FiveThirtyEight.com site projected on Election Day 2016 that Clinton had a 71.4% chance of winning; some prognosticators put it at 90%. Then the unexpected happened, which is why it was unexpected. Unexpected things have happened this year, including the withdrawal of President Joe Biden from the race, two assassination attempts against Trump, and the stunning recovery the Democrats made after late June. It’s still October. October Surprises come in October.

— Between the white vote and the minority vote. The great assumption at the beginning of 2024 was that Trump would be trounced among Blacks and Hispanics. In the end, he may be. But the difference between his 2016 performance and his 2024 potential is telling. Eight years ago, he received 6% of the Black vote and 28% of the Hispanic vote. The vote in 2020 was pretty much the same. Trump now has the support of 14% of Blacks (small, but more than double his 2016 performance) and the backing of 41% of Hispanic voters (a huge improvement). One of the big questions in Milwaukee, Detroit, Pittsburgh, Philadelphia, Atlanta, Phoenix and Tucson is whether Black and Hispanic voters return to the Democratic ticket. If they do, Harris is in a strong position.

— Between the Electoral College and the popular vote. By now, pretty much every American knows that the winner of the popular vote has lost the Electoral College vote twice this century, a matter of renewed controversy about the American political system and fresh doubts about the democratic nature of our politics. Trump lost the popular vote in 2016 by nearly 3 million votes. No matter. This could happen again, though there is new thinking that suggests that the Republican advantage in the Electoral College may be muted this year. Watch this space.

— Between narrative-changing events and a change in the narrative. There’s potential for narrative-changing events everywhere: in racial relations, in the Middle East, in North Korea. Some change the course of an election, as COVID did in 2020. Sometimes they don’t, as in the Johnson administration halting bombing in Vietnam in 1968, which experts thought would boost Hubert Humphrey over Richard Nixon. It didn’t. There are reasons to believe that big events, aside from the departure of Biden from the contest, may not change the 2024 calculus; the assassination attempts against Trump didn’t, and the traditional post-convention popularity bumps both camps expected occurred, though not in dramatic fashion, and they didn’t endure.

— Between what has happened in the past and what will happen this time. Some elections bring dramatic changes in the demographic makeup of the parties. The 1932 and 1936 elections swung blue-collar workers into the Democratic tent — and the 1980 and 2016 elections swung many of them into the Republican tent. We saw college-educated voters, who were basically split between the two parties in the 1980s, begin a significant migration into the Democratic Party 20 years ago. Subterranean movements may be occurring right now, possibly among Jewish and Arab voters, that will be more visible on Nov. 6, when the exit polls are released, than they are now.

— Between the declared winner and the loser who declares victory. We have seen that movie before, and it is a horror film.

A Swampscott High School Class of 1972 member, David M. Shribman is the Pulitzer Prize-winning former executive editor of the Pittsburgh Post-Gazette.