With the 2020 election fast approaching, Michael Chertoff, former Secretary of Homeland Security under George W. Bush and Barack Obama, says three potential nightmare scenarios could play out as Americans head to the polls.

Chertoff, co-founder and chairman of the cyber security risk management firm Chertoff Group, told Yahoo Finance on Friday that he worries about three “buckets” of risk: cyber attacks that could “gum up the works” on Election Day; violence and intimidation; and efforts to undermine the results of the election after the fact.

Cyber attacks could take out polling stations

Chertoff told Yahoo Finance’s “The Ticker” that he fears a cyber attack could take down voting locations, throwing a wrench into the works and deliberately slowing the voting process.

“When people show up at the polls and the poll workers want to check laptops to make sure the person is registered, if a database they are looking to has been attacked with ransomware and it is encrypted and shut down, there’s going to be a significant delay and a real problem,” he said.

“They’ll have to take all provisional ballots, and that will really gum the works up.”

Ransomware, a form of cyber attack, usually spreads through fraudulent emails. When a person clicks a link in the email or opens a document, they inadvertently infect their computer, locking down the entire system and encrypting all of their data. A cyber criminal then contacts the victim and tells them the only way they can get their data back is to pay a ransom.

Of course, cyber criminals are still just criminals, so there’s never a guarantee the attacker will provide a key to decrypt your data. Law enforcement discourages paying any ransom, as it emboldens such criminals.

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Chertoff, however, says that election boards could protect polling stations by having backup systems that are disconnected from the internet, and can’t be hit by online cyber attacks. Poll workers could then turn to those backup laptops if their primary computers are compromised, averting a slowdown at the polls.

Violent actors may attempt to intimidate voters

Beyond cyber attacks, Chertoff says violence could be a serious issue during the 2020 election.

“...I think increasingly, we are getting concerned about the possibility of unofficial, armed groups deciding they want to appoint themself as poll watchers and essentially intimidating people in certain areas to stop them from voting,” he said.

The potential for voter intimidation came screaming to the forefront when President Donald Trump, during the first presidential debate, told a violent, ultra-right wing group, The Proud Boys, to “Stand back, and stand by.”