For months, Bernie Sanders has been pointing to polls that show him performing better in general match-ups against Republicans than Hillary Clinton.

For Sanders, the numbers offer a bold rebuke to skeptics who say that a wild-haired democratic socialist could not win in November. As he’s slipped farther behind in the primary, Sanders has made the polling argument time and again, even arguing that Democratic superdelegates should overlook Clinton’s lead in pledged delegates and raw votes to choose him.

“The Democrats want to see the strongest candidate possible take on Trump or some other Republican,” Sanders told NBC’s Andrea Mitchell on Thursday evening. “At this point, according to the polls, that is me.”

The Vermont Senator beats Republican frontrunner Donald Trump by 14 points while Clinton is ahead of Trump by just 9 points, according to the HuffPost Pollster’s average of polls testing which candidates voters would support in the general election. Sanders beats Texas Sen. Ted Cruz by 13 points while Clinton only beats Cruz by 4 points.

The numbers are accurate, but both Democratic and Republican pollsters say that they don’t mean as much as Sanders says they do.

To be sure, Clinton also makes the case that she would be a stronger candidate in a general election due to her experience and ability to compromise. But Sanders’ emphasis on the polls is misguided, experts say.

General election polls taken months before voting day have a history of being wrong. According to data compiled by FiveThirtyEight, general election polls taken a year in advance have been inaccurate by more than 5 percentage points in the last 10 out of 14 elections for which there is data.

Even polls six months out are inaccurate, too. For example, at this point in the 2000 election, late April polls showed then-Gov. George W. Bush with a strong national lead of five points over then-Vice President Al Gore. Bush lost the popular vote to Gore by half a percentage point that November.

Part of the discrepancy has to do with the early unfamiliarity of the candidates. This year, despite months of frequent coverage on television, social media and the press, Sanders is not as well known as Clinton. A recent NBC/Wall Street Journal poll showed that 56% of Americans say they know Clinton “a lot” while just 38% say the same as Sanders. And while Clinton’s negative ratings may be baked-in after decades in the public eye, Sanders has not received that kind of scrutiny.

In politics, familiarity breeds contempt. If Republicans viewed Sanders as the likely Democratic nominee, he would face negative advertising and intense scrutiny of his record, on everything from his honeymoon in the Soviet Union to his large spending programs. Like any less well-known candidate, Sanders’ unfavorable ratings would rise as people became more familiar with him, pollsters say.

For now, Sanders serves as a kind of stand-in for the Democratic Party, a lesser-known candidate whose popularity reflects the overall favorability of the party, says Stan Greenberg, a veteran Democratic pollster. The Democratic Party is viewed more favorably than the Republican Party, with a favorable-unfavorable rating of about 45-47 compared with 31-58 for the Republicans, according to poll averages. That suggests that in a national race between a generic Democrat and a generic Republican, the generic Democrat would win. At this point in the race, that “brand advantage” benefits Sanders.

“He’s kind of a placeholder for Democrats overall. If you have candidate who is pure and you put them against Trump or Cruz” or another Republican, said Greenberg, he or she has the advantage of being a Democrat.

And in the months ahead of a general election, experts say polled opinions are given cheaply. Poll respondents are asked to tell pollsters who they prefer without the burden of making an actual choice, and voters often react by registering their dislike of a candidate. That’s why protest candidates emerge as early frontrunners: Herman Cain and Newt Gingrich in 2011, and Ben Carson last year. That kind of candidate 0ften fades when voters start to buckle down and think in earnest about who they’d actually like to see in the Oval Office.

This year, Clinton has emerged with unusually high unfavorable ratings in the primary. (The most recent NBC/Wall Street Journal poll found 56% of voters view her negatively, and just 32% hold a positive view.) In head-to-head polls between Clinton and a Republican, pollsters say, a respondent will often simply prefer the “not-Clinton” choice, hurting her in head-to-head match-ups compared with Sanders. Conversely, in a matchup between Sanders and Trump, or Sanders and Cruz, voters may simply prefer the “not-Trump” or “not-Cruz,” benefiting Sanders.

All that makes Clinton look weaker next to Sanders—for now.

“When presented with any plausible choice that seems reasonable, they’re now saying ‘I want to make sure you know, Mr. or Ms. Pollster, if presented with a reasonable choice, I want somebody else’” than Clinton, said Bill McInturff, a Republican pollster. “That expression of ‘I want somebody else’ is not a mature judgment [at this point].”

The head-to-heads may reflect a wide dislike for Clinton at this point in the election. But, “it’s a pretty cheap vote in April compared to when you’re in the ballot box late October or November,” McInturff added.

Sanders’ advisers counter that the polling at this stage is instructive, arguing it shows Clinton’s weaknesses in a general election. Indeed, Clinton receives little support from voters under the age of 30, a fact borne out in primaries across the country as well as recent surveys.

Clinton “has shown no capacity to attract meaningful support from young voters and independents,” said Sanders’ senior strategist Tad Devine in an email. “Bernie has a much better chance of winning back the more traditional base Democratic voters than does Hillary winning indies and young people, and to risk the nomination on her is a real problem for our party.”

And in head-to-heads, Sanders’ advisers say the margin is striking. “Everybody beats Trump, but Bernie really beats him, and does so in key state polling,” Devine said, pointing to Wisconsin. “And Clinton is actually losing to some Republicans other than Trump.”

No matter how the numbers are interpreted, the debate over polling is not just a sideshow.

Clinton has made a forceful case that she is the strongest candidate in a general election against a Republican, resting heavily on her electability as one of the central reasons to pick her as the party’s nominee. “We need a Democratic nominee who will be able to beat the Republicans and get the job done for Americans,” Clinton was telling audiences in New Hampshire in January before voting had even begun.

Her top aides have made the case that the early head-to-head polls that show Sanders leading are not predictive. “These hypotheticals polls among multiple candidates are pretty useless,” Clinton’s strategist and pollster Joel Benenson said in an interview. “There is going to be a contest between two candidates and only two candidates. Anything else is hypothetical and irrelevant.”

Meanwhile, Sanders’ top supporters say that head-to-head polls should play decisive role in the race. Even if Sanders loses the popular vote in the primary to Clinton, Sanders’ backers say, Democratic superdelegates should consider tilting the race toward Sanders if head to-head polls against Republicans remain constant.

“Superdelegates are supposed to make sure we have candidates that can win. … If the assessment is that Bernie can beat these guys pretty good, then they should be thinking long term about the party,” said Rep. Raúl Grijalva. “I think head-to-head polls should be a consideration.”

But even many of Sanders’ most ardent supporters do not believe he’d be the best candidate to face Clinton in a general election. In Wisconsin, where Sanders trounced Clinton by a 14-point margin, a CNN exit poll showed that 54% of voters believed that it was Clinton who had a better chance of beating Donald Trump in November.

If history is a guide, early general election head-to-head polls can only say so much. “Pollster aren’t making predictions. They’re trying to determine the state of the race right now,” said Jennifer Necci Dineen, a pollster and faculty member at the University of Connecticut. “Six months from now is even still a little bit early.”

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