Among dozens of scenarios being contemplated by the companies for election night in particular are a "hack and leak" operation where stolen materials are quickly spread through online networks and addressing the distribution of manipulated videos, according to a person involved in the planning who spoke anonymously so as to not speak on behalf of the full industry coalition. The scenario planning is "candidate agnostic," they said.

Today's statement comes shortly after a meeting among the companies and government officials — the Cybersecurity and Infrastructure Security Agency, the FBI’s Foreign Influence Task Force, the Department of Justice's National Security Division, and the Office of the Director of National Intelligence — to discuss the planning. It builds on a series of monthly meetings, the person said, that go back to September of last year.

Why Silicon Valley gaming out 2020 matters: Google, Facebook, Twitter and other social platforms became key vectors for election meddling in the United States in 2016, and here the companies are addressing went wrong back then, like the hacking of emails tied to the Clinton campaign and Democratic National Committee. But the companies are also looking at what makes 2020 unique; whether there's a winner on election depends both the role played by mail-in ballots triggered by Covid-19 lockdowns and candidates' willingness to concede, and Trump has laid the groundwork for declaring the results invalid.

Why the statement is eye-catching: The document is unusual because the tech companies are often extraordinarily competitive with each other. In some cases, the executives simply don't like each other. And the companies have taken different approaches to what to allow on their platforms. Their individual rules and decision-making still apply, but they close coordination allows them to share both lessons learned and ID threats coming down the pike. That's key because one of the critical lessons learned in recent years is that problematic content often spreads across platforms, so combining forces helps the companies amplify their efforts.

Also, the companies' close coordination with government agencies — namely DHS and the FBI — stand in stark contrast to 2016. The lack of public-private communication led many in Silicon Valley to believe that the industry got thrown under the bus by a national security and law enforcement community that had itself missed the threat posed by Russia.

Why it may not be enough: Catching misinformation quickly to prevent it from influencing elections is a challenge. Critics say the social media companies have waited too long to start efforts like this and may find that it is too late to put the necessary safeguards in place.

What's next: The companies will stick with disaster planning in the lead-up to Election Day, when their preparations will get tested in the harsh glare of one of the most controversial elections in U.S. history.

Steven Overly contributed to this report.