The start of the Senate hearing saw the sort of person the social media giants contend with in the form of Mr Alex Jones, the conspiracy theorist with a considerable following, whose radio show has recently been taken off platforms like YouTube and Facebook.
Top Twitter Inc and Facebook Inc executives will defend their companies before US lawmakers on Wednesday, with Facebook insisting it takes election interference seriously and Twitter denying its operations are influenced by politics.
The statement did not name Facebook Inc and Twitter Inc but the companies have been criticized for what some see as an effort to exclude conservative voices.
"It is definitely a violation and we were slow to act", Dorsey said.
Google was also invited to attend the Senate hearing but declined to send its chief executive Sundar Pichai or parent firm Alphabet chief Larry Page.
Facebook and Twitter are using increasingly sophisticated technology and artificial intelligence to combat the misuse.
The afternoon hearing before the House Energy and Commerce Committee was to focus on bias and Twitter's algorithms.
Also on Wednesday, Facebook founder Mark Zuckerberg in an op-ed piece in the Washington Post, wrote: "It's an arms race, and it will take the combined forces of the USA private and public sectors to protect America's democracy from outside interference".
The companies have conveyed to the commission that all sponsored content in favour of a political party, political leader or candidate will flag the concerned sponsor and the amount paid for posting the content on Facebook, WhatsApp (owned by Facebook), Google or Twitter.
"We need to seriously think about whether the time has come for these companies to abide by new transparency obligations", Pai said in a blog post. However, Facebook COO Sheryl Sandberg told the committee that the company was continuing to fight misinformation, fake news, and foreign interference. Mark Warner, D-V.A., said in his opening remarks Wednesday morning.
In a written statement, Google chief legal officer Kent Walker promised to maintain efforts to thwart foreign interference in United States elections.
Only Dorsey was invited to the House hearing after specific Republican concerns about bias on Twitter.
Twitter's Dorsey also will testify at a House of Representatives hearing on Wednesday that the company "does not use political ideology to make any decisions", according to written testimony also made public on Tuesday.