Reporting on the audit of the 2020 presidential election now going on in Maricopa County, Arizona, National Memo’s Steven Rosenfeld writes that one floor observer was overheard saying, “I hope they are fake ballots, because I am seeing so many Biden.”

After the November 7 election, Trump supporters wondered how Biden could possibly have won when all they’d seen for months were reports of packed Trump rallies, yards filled with Trump signs, and excited Facebook posts about Trump and his upcoming win.

They were honestly shocked when Trump lost. They simply couldn’t connect up their own experience with the result of the election. They live within a right-wing echo chamber where opposing viewpoints are rarely heard. They saw the widespread support for Biden only through the lens of right-wing misinformation and disinformation. They dismissed Biden’s continual lead in the polls as “fake.”

Facebook, the go-to social media platform for Trump supporters in 2020, did a lot to contribute to the echo chamber. When the social network’s algorithms pick up on a user’s interest in right-wing content, it serves them more and more of it, and filters out other opinions. All through the campaign, many Trump supporters saw nothing but news posts and shared memes about Trump’s achievements as president, his huge rallies, and his mockery of Joe Biden and the Democrats.

And right-wingers were, and remain, the most energized group on Facebook, even as Donald Trump remains expelled from the platform after he helped incite an insurrection on January 6.

The top-performing link posts by U.S. Facebook pages in the last 24 hours are from:

1. Dan Bongino
2. Franklin Graham
3. Dan Bongino
4. Ben Shapiro
5. Ben Shapiro
6. Ben Shapiro
7. Dan Bongino
8. Newsmax
9. Ben Shapiro
10. Forbes

— Facebook's Top 10 (@FacebooksTop10) May 24, 2021

The disappearance of local news sources is also contributing to Americans’ politically homogenous media diet. Local newspapers and TV affiliates are often no longer present in the community to report on diverse subjects and opinions. In the absence of that coverage, community members are often left only with national news sources. In red America, that means Fox News, which did its part to sow doubt in the election result.

Partisan segregation, online and off, may explain Trump supporters’ shock in the week after November 7, 2020, when it became clear Biden had prevailed. It helps explain how Donald Trump was able to sell the Big Lie that he’d won. People were ready to believe it—it provided an explanation for an election result that didn’t make sense. In fact, 60% of Republicans still say that they believe Trump to be the real winner of the election.

The audit in Arizona shows that red America is not letting go of the Big Lie easily. There are now plans for a similar audit in Fulton County, Georgia. And belief in the Big Lie has provided political cover for Republicans in state government to take big leaps forward in advancing new voting restrictions.

The media has enabled the formation of two separate media universes that portray two separate political realities. Democracy is a team sport, but Republicans and Democrats are increasingly unable to even meet on the same playing field. As long as information gatekeepers such as Facebook and Fox continue to profit from partisan filter bubbles, they’ll continue enabling them.