Exactly twelve years ago, on July 29, 2007, national opinion polls declared the front-runner for the Republican Presidential nomination to be one Rudolph Giuliani, the bombastic former New York City mayor. In second place, seven points back, was a retired Tennessee senator and actor, Fred Thompson. Languishing in third place, another five points behind, was the eventual G.O.P. nominee, John McCain. Over on the Democratic side, on the same date, Hillary Clinton led Barack Obama by nearly thirteen points. Everyone knows how that turned out.

Twenty Democratic candidates are set to debate in Detroit this week, as countless Democratic voters wonder, with knotted stomachs, whether anyone will emerge to defeat Donald Trump, in November, 2020. So what do the early polls tell us? I asked around and found an array of specialists firm in their beliefs that the polls are iffy. “These numbers are fun, but I wouldn’t put money on anything,” Lydia Saad, a senior Gallup research director, told me. “Historically, among Democrats, if you had to bet at this point, you’d do a better job betting against, than for, the front-runner.” Which can’t be good news for Joe Biden, who is ahead but who slipped after his shaky debate performance, last month.

Jim Messina, Obama’s campaign manager in 2012, didn’t mince words: “Right now, it’s just too bumpy. There are too many candidates. There’s too much back-and-forth. ‘Oh, the polling shows Joe Biden is the best candidate to win the election.’ And then, after the first debate, ‘Oh, Kamala Harris came up, and she can win.’ And all of it is just bullshit.” At this stage, he said, polls can offer indications of what might happen, but he wouldn’t take them to the bank. One problem is that so little is known about so many of the Democratic candidates. Another is that so few people are paying close attention. And then there is the fact that a Presidential campaign is a bruising, billion-dollar proving ground. No candidate sails to victory untested and unscathed.

Soon after Biden entered the race, in late April, polls showed him to be far ahead of a trio of senators from blue states: Bernie Sanders, of Vermont; Elizabeth Warren, of Massachusetts; and Harris, of California. But Biden’s initial lead over Sanders, of twenty to thirty points, has dwindled to an average lead of about fourteen points, with Warren and Sanders roughly tied for second and Harris close behind, according to an aggregation of national polls compiled by Real Clear Politics. The next-closest competitor is the South Bend, Indiana, mayor, Pete Buttigieg, who remains in single digits. No other candidate reaches even three per cent.

A significant portion of the support for Biden and Sanders can be attributed to name recognition. More than eighty-five per cent of Democrats and Democratic-leaning Independents had opinions about the two men, Gallup reported this month, and about seventy per cent saw each favorably. Only forty-nine per cent had an opinion about Julián Castro, fifty-three per cent about Buttigieg, fifty-seven per cent about Cory Booker, and sixty-five per cent about Harris, leaving lots of room for these lesser-known candidates to define themselves. Their challenge is to be noticed, positively. History shows that it can happen. “The Democratic Party tends to try to kill off its front-runners,” Jeremy Rosner, a managing partner at GQR, a prominent Washington-based polling and strategy firm that works with progressive candidates, said. “We saw with the first debate how quickly things can change. One good performance, one scandal, one misstep. Right now, boy, my feeling about the Democratic field is: Who the hell knows? Almost all of them are really impressive, and in almost all of them I can see their liabilities and how they get defeated.”

Campaign ledgers are littered with candidates who once surged to the lead in a Presidential-nomination contest, only to fade. A short and incomplete list would include Joe Lieberman, George Wallace, Jesse Jackson, Chris Christie, Jerry Brown, and Jeb Bush. Yet, though polls may have limited predictive power early in the game, they are hardly worthless, John Sides, a professor of political science at George Washington University, told me. “There’s some signal in the noise. People polling in the double digits really do have different odds of winning than candidates polling at one or two per cent,” Sides said. “You can’t dismiss the polls out of hand as not telling you something informative. On the other hand, they’re not necessarily going to pick the winner at this point, nor can they tell us what changes might happen.” Four candidates are currently polling in double digits: Biden, Warren, Sanders, and Harris.

When Sides refers to changes, he means calamities that could befall a candidate, through a scandal or an origin story that doesn’t add up. Think of the Democratic front-runner Gary Hart and his alleged affair, during the 1988 campaign, aboard the good ship Monkey Business. Or Ted Kennedy, who challenged an incumbent President, Jimmy Carter, and led him in the polls, only to stumble when asked, by Roger Mudd, in a televised CBS interview, “Why do you want to be President?” In another interview, Tom Jarriel, of ABC, brought up the past: “Senator, you cheated in college. You panicked at Chappaquiddick. Do you have what it takes to be President of the United States?”

All of those moments, of course, preceded the rise of Trump. On July 1, 2015, two weeks after he rode down an escalator at Trump Tower and entered the race, he was polling at six per cent, according to the Real Clear Politics average. A month later, he was leading the field, with more than twenty-one per cent of the total. From then on, all the way to the G.O.P. nomination, Trump met outrage with umbrage and trailed for only an instant. He launched his campaign by calling Mexican immigrants “rapists.” He cast critics as unpatriotic losers and working journalists as enemies of the people. He mocked John McCain, a former Navy pilot, for being captured during the Vietnam War. He told supporters at a rally that he’d like to punch a protester in the face. He refused to release his tax returns. He boasted about grabbing women’s genitals. He denied the accusations of more than a dozen women who said that he had groped them. And he barely lost his stride.

During the 2016 primaries, Trump, in his inimitable way, solved the same sort of publicity challenge currently faced by this year’s Democratic candidates. He captivated audiences and kept the attention of the media by inventing belittling, yet memorable, nicknames for his fellow-candidates and turning, without shame, to what he liked to call “truthful hyperbole,” which fact checkers now more commonly identify as lying. (“It may not be good for America, but it’s damn good for CBS,” Les Moonves, who was then the network’s chairman, crowed. He reported, in February, 2016, that “the money’s rolling in and this is fun.”) As a matter of marketing and political science, the formula worked like magic beans for Trump’s chances. “The general rule is that voters don’t change their minds without information,” Sides explained, adding, about the current Democratic field, that “to get information in a twenty-three-candidate primary is largely a function of news coverage. To get news coverage is to do something newsworthy. It’s a very self-reinforcing cycle.”