So what you do is say you think some American is a Russian Agent and just like that you can get a warrant for surveillance. And that is how you surveil the Trump Campaign.
According to 24/7 News, a new report shows that the FBI got a warrant to surveil a former Trump campaign adviser over possible ties to Russia. The "Washington Post" reports that the FBI and Justice department showed a Foreign Intelligence Surveillance Court judge that there was probable cause to think Carter Page was acting as a Russian agent. The warrant was part of the FBI's investigation into Russian interference in the 2016 presidential election. That probe includes looking into possible ties between Russia and the Trump campaign.
In response to the report, Carter Page said it confirms his suspicions of "unjustified, politically motivated government surveillance." He also compared it to the FBI's monitoring of Martin Luther King Jr.