Russian attempts to use social media to disrupt U.S. politics came home to Minnesotans recently with the revelation that Russia-linked Facebook accounts may have been used to aid a protest for Philando Castile in July 2016.

According to the Wall Street Journal, the “Don’t Shoot” Facebook account was just one of several that was involved in at least 60 rallies, marches and protests across the country, even helping to finance some via bank cards or money transfers. Local protest organizers contacted by the Star Tribune have disavowed any knowledge of any Russian involvement. Some suspected at the time that the “Don’t Shoot” account was a front for outsiders.

These efforts are corrosive to a democracy. They take the old, 1960s fear of “outside agitators” to a new level. Disrupters need never be physically in the space they seek to destabilize. They can change the tenor of the national conversation by planting stories and fake ads, using “bots” to throw verbal hand grenades into online discussions. The “Don’t Shoot” account appears to have been easy enough to set up. It led to a defunct website, and the phone number rang to a fax machine.

Analysts say Russian accounts are attempting to increase hostility in the U.S. Their inflammatory posts and ads get shared, commented on, amplified. If American society seems angrier and more fractious than ever — which by itself can contribute to unease — at least part of that can be traced to those who are intentionally cultivating such division. One group called “Being Patriotic” in 2016 was posting that Black Lives Matter activists who did not respect the American flag should be summarily shot. That account gathered 200,000 followers before it was shuttered.

Social media has been a boon to many, connecting the world. People enjoy the ability to easily communicate with loved ones, reconnect with old friends and find new ones with similar interests. Since its inception in 2004, Facebook has become a conglomerate, with 2 billion active users who communicate in 140 languages. But it also has become a sophisticated propaganda tool in the hands of those who would do this country harm.

As these techniques become more polished, strategies must be developed that will protect the cherished right to free speech that underpins American society, while guarding against malevolent intent. A key element of that should be the tried-and-true disinfectants of disclosure and rigorous fact-checking. Facebook and others must undertake greater voluntary efforts to vet those who use their sites.

Democratic U.S. Sen. Amy Klobuchar has teamed with Republican U.S. Sen. John McCain and others on a bill that would require stronger disclosure rules for paid political ads on social media sites. Companies such as Facebook, Google, Twitter and others would be held responsible for making reasonable attempts to determine whether ads were funded by foreign interests. Facebook CEO Mark Zuckerberg has already agreed to do so. Others should follow suit, and Congress should ensure it.