On Friday, Americans got their second “October surprise” of the presidential election. The first was the Access Hollywood tape in which Donald Trump boasted of sexual assault. This one was less evocative but still shocking: a letter from FBI Director James Comey on the investigation into Hillary Clinton’s private email server.

Initially, this looked explosive. “In connection with an unrelated case, the FBI has learned of the existence of emails that appear to be pertinent to the investigation,” Comey wrote to Republican congressional committee chairmen. “I am writing to inform you that the investigative team briefed me on this yesterday, and I agreed that the FBI should take appropriate investigative steps designed to allow investigators to review those emails to determine whether they contain classified information, as well as to assess their importance to our investigation.”

According to U.S. Rep. Jason Chaffetz, chairman of the House Oversight Committee, the FBI was “reopening” the investigation. But this was wrong. Subsequent reporting filled in details. Having told Congress that he would keep them abreast of developments in the Clinton case, Comey was obligated to send them this letter. The emails didn’t come from Clinton; there was no withholding of evidence from either Clinton or her campaign; and the emails themselves came from outside her server. Specifically, the FBI retrieved them from a device used by Anthony Weiner, as part of its investigation into his allegedly sexting an underage girl.

That leaves us with the politics of the revelation. How will it affect the election? Could the mere mention of “emails” change perceptions toward Clinton? When the news first broke, conservative commentators were sure that this would change the shape of the election. “This is not good for Team Clinton,” said Josh Kraushaar of National Journal. One vocal commentator, Matt Mackowiak, insisted that this “must be very serious” and that the uncertainty of it all was “politically lethal.”

At this stage, we have no idea how this development will shape the last 11 days of the presidential race. Tens of millions of Americans have already voted in battleground states like North Carolina, Florida, Texas, and Nevada. Given the effect of past email news, it’s possible this will turn off independent or undecided voters from Clinton. It’s also possible that her negatives are already baked in and won’t budge. And it’s possible, perhaps likely, that it won’t matter at all.

Everyone agrees that American politics is more partisan and more polarized than it’s ever been. But not everyone grasps why that’s important. It’s not just Congress and the ability of our institutions to make progress and accomplish their goals. It’s also our elections.

The folk theory of American democracy is that citizens deliberate on the issues and choose a candidate. That is false. The truth, as political scientists Christopher Achen and Larry Bartels describe in Democracy for Realists: Why Elections Do Not Produce Responsive Government, is that voters are tribalistic. Their political allegiances come first, and their positions and beliefs follow. We’ve seen this with Donald Trump. Support for free trade is a longstanding belief within the GOP, but Trump is a major opponent, slamming most of the trade deals of the past 30 years. You would think that this would depress his support among Republican voters. It didn’t. Instead, those voters changed their views of trade. Their beliefs followed their affiliations, not the other way around.

When it comes to elections—or at least, presidential elections—this leads to an important conclusion: What a candidate believes is less important to voters than his or her partisan affiliation. Trump has passionate supporters who believe in his message of ethnonationalism and racial exclusion. But the reason he’s a stone’s throw from the White House isn’t because he’s convinced 50 million Americans that he’s right. The reason Trump is relatively close is that he’s the Republican presidential nominee, and in a partisan, highly polarized country, that’s enough. In the past four presidential elections, major party nominees have won the vast majority of co-partisans—upward of 90 percent. Simply having the nomination is sufficient to put anyone in firing distance of becoming president, regardless of larger circumstances or events or personality deficiencies.

There are still battles to fight, but they happen on the margins and involve a small share of voters. This polarization is so strong, in fact, that it renders the gaffes and incidents of recent elections almost irrelevant. Mitt Romney’s remarks on the “47 percent” in the 2012 election were bombshells that changed the immediate landscape of the election. But a month later, the effect had died down. In a real way, it didn’t matter. Again, we’ve seen the same with Trump. Scandals affect his numbers, but he always recovers, as Republicans return to his camp. It’s even happening now, as GOP voters look past the Access Hollywood tape to line up behind the real estate mogul.

If the final week of an election is a time of mass mobilization and hyperpartisanship, then the best odds are that the Weiner emails—and the renewed focus on Clinton’s email server—won’t matter. Indeed, that’s what it means for an electorate to be polarized. Whether pundits even begin to understand that is a separate question.

Read more Slate coverage of the 2016 campaign.