“They’ve built defenses for past battles, but are they prepared for the next front in the war?” Laura Rosenberger, the director of the Alliance for Securing Democracy, a think tank that works to counter foreign interference campaigns, said of the tech companies. “Anytime you’re dealing with a sophisticated actor, they’re going to evolve their tactics as you evolve your defenses.”

By most accounts, the big tech companies have gotten better at stopping certain types of election meddling, such as foreign trolling operations and posts containing inaccurate voting information. But they are reluctant to referee other kinds of social media electioneering for fear of appearing to tip the scales. And their policies, often created hastily while under pressure, have proved confusing and inadequate.

Adding to the companies’ troubles is the coronavirus pandemic, which is straining their technical infrastructure, unleashing a new misinformation wave and forcing their employees to coordinate a vast election effort spanning multiple teams and government agencies from their homes.

In interviews with two dozen executives and employees at Facebook, Google and Twitter over the past few months, many described a tense atmosphere of careening from crisis to crisis to handle the newest tactics being used to sow discord and influence votes. Many spoke on the condition of anonymity because they were not authorized to publicly discuss sensitive internal issues.

Some Facebook and Google employees said they feared being blamed by Democrats for a Trump re-election, while others said they did not want to be seen as acting in Democrats’ favor. Privately, some said, the best-case scenario for them in November would be a landslide victory by either party, with a margin too large to be pinned on any one tech platform.

Google declined to speak publicly for this article. Nathaniel Gleicher, Facebook’s head of cybersecurity policy, said the threats of 2016 were less effective now but “we’ve seen threat actors evolving and getting better.” Twitter also said the threats were a game of “cat and mouse.”

“We’re constantly trying to stay one step ahead,” said Carlos Monje Jr., Twitter’s director of public policy.