(CNN) The Democratic National Committee warned presidential campaigns on Monday of "heightened disinformation and discourse manipulation activity" around the Democratic debate hosted by CNN and The New York Times .

CNN has previously reported how Russian government-linked trolls were active online during debate nights in 2015 and 2016, but the DNC's warning also included what it views as a domestic disinformation threat: the Trump administration. The committee described the White House's current strategy on impeachment "as a broad Republican disinformation campaign."

The DNC's warning was based on activity it had observed around previous debates that had the goal of "polarizing opposing Democratic supporters."

CNN obtained a copy of the warning, which was first reported by Politico.

Since it was hacked during the 2016 campaign, the DNC has hired staff, including some former Silicon Valley executives, to help shore up the party's cyberdefenses. CNN previously reported that this effort has extended to initiatives to monitor and tackle online disinformation. The DNC has set up a small team to monitor disinformation and is in regular communication with the social media platforms.

"When contemplating a response to disinformation narratives, campaigns should consider whether misinformation has reached a tipping point where the costs of ignoring the issue are higher than the costs of the amplification that a response might generate," Monday's email from Bob Lord, the DNC's security chief, read.

"When misinformation has reached a tipping point, aggressive responses to misinformation that seek to reframe the debate tend to be most effective."

The email provided details for contacts at the main social media companies and also encouraged campaigns "observing inauthentic or suspicious activity" online to report it to the DNC.

Lord's email also referenced Facebook's policy of allowing political candidates, including the Trump campaign, to run ads that include lies.