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Russian President Vladimir Putin.
The White House and the Department of Homeland Security are leading the effort against Russian cyber-meddling, government officials told NBC
One "worst-case scenario" the officials envision is a cyber-attack that shuts down part of the internet. Such an attack could mirror last month's hack that temporarily knocked out a number of popular websites including Twitter, Spotify, and PayPal - an attack some security experts think was conducted by Russia as a "dry run" for an Election-Day hack.
Other less-severe operations could include the release of fake documents that could damage one of the candidates without giving the media a chance to fact-check them. In October, the US government accused Russia of hacking Democratic Party organizations, leading to the release of thousands of illegally-obtained emails that have damaged Democratic candidate Hillary Clinton.
Clinton has said that Russia is trying to get Republican nominee Donald Trump elected, and called Trump a "puppet" of Russian president Vladimir Putin.
"Given [the Russians'] past behavior in other contexts, we understand the way they like to go about potentially causing confusion and so we want to make sure that we are mitigating that potential," a Department of Homeland Security official told NBC News.
As for actually altering the vote count on Election Day, that task would be extremely difficult for hackers, the officials said, because of the "decentralized nature" of US elections.
"States ensure that voting machines are not connected to the Internet, and there are numerous checks and balances as well as extensive oversight at multiple levels built into our election process," an senior administration official told NBC News.