For months now, commentators and political insiders have been making various arguments about why Donald Trump can’t win the Republican Presidential nomination: he’s too extreme; he has no political experience; his campaign will eventually implode; the rest of the Party will unite against him; he’s just a protest candidate; and so on. As we draw closer to the start of the primaries and Trump’s lead in the national polls persists, some of these arguments are still being put forward, if not with quite so much vehemence. But another skeptical case is being made about Trump’s prospects, which goes like this:

Many of Trump’s supporters are disaffected folks who are only marginally attached to the political process. A good number of them won’t show up at the voting booths. So despite the fact that none of the other candidates has been able to overtake him, the polls are overstating his support and understating the probability that he won’t get the nomination. “The ‘who’ that will defeat Trump is not another candidate, but is most likely to be the Republican voters who actually turn out in Iowa, New Hampshire, South Carolina, and the other contests,” Alfred J. Tuchfarber, the founder of the respected Ohio Poll, wrote earlier this week in a guest post for Sabato Crystal Ball. “About 75%-80% of the Republican primary voters in the early states are not likely to vote for Trump.”

Tuchfarber, an emeritus professor of political science at the University of Cincinnati, pointed to an interesting discrepancy that has emerged in recent polling in Iowa and South Carolina. Some pollsters, in sampling for people likely to vote in the Republican primaries and caucuses, include all voters who are registered Republicans. The polls that apply this screen, which include those from Fox News, Quinnipiac University, and CNN, have tended to show Trump doing well. But other polls, including those from Monmouth University, Winthrop University, and the Des Moines Register/Bloomberg, apply additional screens, such as only questioning those Republicans who have voted in previous primaries or who express a strong interest in the race. And these polls tend to show considerably lower numbers for Trump.

For example, the latest Quinnipiac poll in Iowa, which applied the broader screen, showed Trump with a narrow lead over Ted Cruz: twenty-eight per cent to twenty-seven per cent. The most recent Des Moines Register/Bloomberg survey, which applied the tighter screen, showed Trump trailing Cruz by ten percentage points: twenty-one per cent compared to thirty-one per cent. This phenomenon is also evident in South Carolina, where the third G.O.P. contest will be held. A recent Fox News poll there showed Trump with a twenty-point lead over the second-place Ben Carson, while a Winthrop survey had Trump ahead by just eight points, with Cruz in second place.

Which methodology is the right one? “The Monmouth and Winthrop polls use sampling methods that are about as good as a pollster can use at this point in the process,” Tuchfarber wrote. He argued that the pollsters whose surveys show Trump with a big lead are implicitly assuming that all registered Republicans turn out to vote, which is unrealistic, particularly in Iowa, where voting in a caucus is a lengthy process. Much of Trump’s support comes from blue-collar voters, he said, calling them “substantially less likely to actually turn out than are upscale voters, especially in caucuses, but also in primaries.” Tuchfarber went on: “Trump’s true level of support is much more likely to be near the Monmouth, Selzer, and Winthrop estimates. That puts him in the 20%-25% range, not 30%-35%.”

As an experienced pollster—the Ohio Poll has a good record of forecasting state elections—Tuchfarber’s views demand to be taken seriously. Other savvy analysts, such as the Times’s Nate Cohn, have put forward a similar argument. Indeed, I’ve also heard it made by people close to the Clinton campaign, who continue to believe that Marco Rubio or Ted Cruz will emerge as the G.O.P. candidate.

The argument that the polls are overstating Trump’s support isn’t necessarily true, however: there are at least two counterarguments being made to suggest that the polls might actually be understating Trump’s lead.

The first one relies on the fact that, in some states, voters in the G.O.P. contests don’t need to have registered previously as Republicans. In Iowa, for example, they can register on the night of the caucus. In the New Hampshire primary, voters who aren’t registered as Republicans or Democrats are eligible to vote. The Trump campaign, in appealing to people who didn’t previously vote, or who aren’t registered with either party, might be expanding the G.O.P. electorate in a manner that some of the polls aren’t fully picking up.

Arguably, that is what President Barack Obama did in Iowa in 2008, when turnout in the Democratic caucus was considerably higher than expected, and he beat Hillary Clinton by eight points. “Eight years later, Republicans may have their own version of the Obama campaign in the form of Donald Trump,” Jordan Gehrke, a Republican political strategist, wrote in a piece for National Review. “He’s the only candidate with anything like Obama’s celebrity appeal—and knack for reaching voters who don’t normally go to the polls.” Gehrke suggested that if Trump invests in a proper ground operation to get these new voters to the polls, he could well pull off a win in Iowa or New Hampshire, despite the opposition of the Republican establishment. And, he wrote, “Coming off a victory in one of the first two states, Trump could be unbeatable precisely because he will have won by turning out a new coalition loyal only to him.”

The other factor to consider is that some Republicans may be reluctant to tell pollsters that they are supporting Trump. The thinking here—often referred to as the “shy Tory” theory, because it appears to have applied in recent years to the Conservative Party in Britain—is that voters may be too embarrassed to acknowledge their support for candidates or parties that are considered controversial or hard-hearted. But when these voters get into the privacy of the voting booth, they express their true preferences. Citing an American example of how this process can work, Gehrke pointed to former Senator Jesse Helms, of North Carolina, who “was left for dead more than once by pollsters and won anyway.”

So which is it? Are the polls overstating or understating Trump’s support? The nature of these things makes it hard to say. But in a little more than seven weeks, the Iowa caucuses and New Hampshire primary will both be done, and we will know the answer.