The suspicious package sent to the Kentucky home of Republican Senator Rand Paul contained a threatening letter and a substance that appears to be non-toxic, according to the Warren County Sheriff’s Office.

The package arrived at the Paul family home in Bowling Green Monday morning. The package was taken to the Bowling Green Fire Department, where a preliminary analysis showed the substance, which was not identified, was not lethal.

Paul is a popular target on social media for his outspoken views and his penchant for grandstanding and picking fights with Dr. Anthony Fauci during senate hearings. He recently made headlines for saying he won’t be getting the COVID-19 vaccine because he feels he has natural immunity from having had the virus last year.

After the package arrived, Paul’s wife wrote on twitter that she had received “the death threat letter” and alerted the FBI. The bureau has reportedly launched a probe into the incident. The story took a strange turn as the senator blamed a tweet from pop star and songwriter Richard Marx for inspiring someone to send the package. Marx’s tweet, which has been deleted for violating twitter rules, said he would buy drinks for Paul’s neighbor, who broke the senator’s ribs during a 2017 assault.

Marx fired back to critics who agreed with Paul by noting that, like most Republicans, Paul was stone-cold silent for four years as then-president Trump tweeted all sorts of dangerous rhetoric.