I wrote last week that Ron DeSantis is not Scott Walker, largely because Mr. DeSantis already has impressive poll strength.

But it’s fair to wonder if we should really be worrying about that at this early stage. After all, there’s still almost a year left until the main season begins in earnest.

Believe it or not, we probably should. Even at this early stage, the polls are often surprisingly indicative of the final outcome of presidential primaries.

The leader in polls conducted in the first quarter of the year before the primary has won the nomination the most times in the era of modern primaries, dating to the 1970s. They usually succeed another candidate with significant support in early polls.

Put it together and there’s a decent ratio between early polls and the outcome of the presidential primary, a ratio that bodes well for Mr. DeSantis. (Higher quality surveys have tended to show less support for Donald Trump).

Of course, that relationship is far from perfect. But consider how much time is left until the start of the primary season. At this point, most of the candidates have not even announced their candidacies. No one has stepped on the debate stage. And yet, poll results already predict the bottom line with astonishing regularity.

If you’re serious about the value of early polls, there’s an equally startling implication in the way you think about presidential primaries: The campaign is already halfway through, even though it looks like it hasn’t even started yet.

Upcoming speeches, debates, and announcements matter just as much as what’s already in the rearview mirror.

The idea that the campaign is already at halftime is a bit mind-boggling, but if you reimagine a presidential campaign as everything a candidate will do to amass the support needed to win, it starts to make a little more sense. Most winning presidential primary campaigns are based on support garnered long before the actual campaign begins.

Take a clear recent case: Joe Biden in 2020. When did he get the support he needed to win the nomination? He won black votes in South Carolina with soaring speeches on the campaign trail? Did he win him in the debates? He won him with television advertising? Did he build his relationship with James Clyburn, the former Democratic majority whip and kingmaker from South Carolina, over a night of dinner and drinks in February 2020? Of course not.

Biden earned their support long before the campaign began, when he was Barack Obama’s loyal vice president for eight years. Without the goodwill he amassed leading up to the campaign, he would most likely have started and finished with minuscule support in the polls, just like his previous two presidential campaigns.

The idea that Biden’s support was mostly built before he entered the race is probably not too surprising. What is more telling is that this early support often seems to be enough to win a presidential nomination.

In the modern era, only two candidates, George Wallace in 1976 and Gary Hart in 1988, entered the primaries with more than 20 percent support and then the nomination went to a candidate who started with less than 20 percent support. Neither example offers much of a precedent for the typical unlikely candidate: Mr. Hart dropped out of the race amid accusations of spousal infidelity; Wallace built his career as a segregationist and opposed large sections of the Democratic Party.

Of course, many long shot candidates have emerged from obscurity to become serious contenders in the face of strong competition. Mr. Hart may have lost to Walter Mondale in 1984, but he came close enough to set an unequivocally strong precedent for long-shot contenders, even in defeat.

In more recent years, the rise of the Internet and cable news has helped more than a dozen candidates with initially limited support reach the top 20 percent in national polls, including Donald Trump, Bernie Sanders, Ted Cruz, Elizabeth Warren, Newt Gingrich, Howard Dean, Rick Perry, Herman Cain, Mike Huckabee, Wesley Clark, Fred Thompson, Mitt Romney (in 2008) and Ben Carson. A handful of these candidates ultimately put up a strong fight, but only Trump won the nomination.

Why does early support seem to indicate so much about a candidate’s outlook? The simplest interpretation is that candidates with early support in the polls have many advantages over other candidates in the search for the nomination.

Part of that advantage may simply be that these tend to be good candidates. Not only are they stronger in quality than the typical latecomer, but their support may be more enduring. After all, it’s not easy to attract mass support for a presidential candidacy long before the nomination race, when neither the media nor voters are paying much attention.

To get to 20 percent before the campaign season, Obama had to give one of the most notable political speeches of the last half century; to reach 20 percent during the campaign season, Mr. Perry did not have to do much more than receive several weeks of press coverage that would never have been devoted to his candidacy a year earlier.

Virtually all of the early poll leaders were well-established national political figures. They may not have been great speakers, but they had other strengths. They had already been investigated. They had already earned the trust of many voters. They had vast, elite support networks, leading to strong fundraising, experienced staff, and high-profile endorsements.

They often possessed more than mere name recognition: a deeper kind of familiarity that makes them the “default” choice for voters who don’t fall for another candidate, a description that fits John McCain in 2008 and the Mr. Biden in 2020. These well-known candidates often have little to prove.

Another reason for the success of early adopters is that initial strength itself confers important advantages, regardless of the quality of the candidate. Its strength can be enough to deter strong opponents. They lock up donors and staff who might otherwise have gone to the competition. They are almost guaranteed constant coverage from the media outlets that less well-known candidates are desperate to attract for themselves. As a result, they can put on exhaustive debate performances that would be woefully insufficient for candidates hoping to come out of obscurity.