He was one of the first to study the role of the Internet in presidential campaigns during the 1996 election. For the 2004 election be began examining how people used blogs and their role in the campaign. For the 2008 election, Johnson focused on social network sites and by 2016 he was examining the role of mobile news applications. Johnson's research has focused on media credibility, selective exposure and uses and gratifications of various social media. Currently he exploring what influences people to hold misperceptions and conspiracy theories toward the coronavirus and toward the 2024 election.  He is co-editing a book examining ways news organizations can improve their coverage of threats of democracy and how existing practices contribute to those threats.