A suspicious package containing white powder was sent to the home of Sen. Rand Paul, R-Ky., his office said Monday. Investigators later determined the substance was not hazardous, a law-enforcement source told NBC News.
"I take these threats immensely seriously. As a repeated target of violence, it is reprehensible that Twitter allows C-list celebrities to encourage violence against me and my family," Paul tweeted.
The suspicious package, which was sent to his Kentucky home, contained a white powder, his office told NBC News. The envelope examined for harmful substances and investigated by the FBI and Capitol Police.
The law enforcement source said initial testing of the substance determined it was not dangerous. In a statement, the Capitol Police said that as a precaution, the substance is being take to a lab "for further testing."
“This is an open investigation,” the statement said.
It was not immediately known whether Paul was in Kentucky when the package arrived. His wife Kelley Paul, tweeted that "I got the death threat letter and called the FBI."
Both she and her husband blamed pop singer Richard Marx for "inciting violence" against him.
Marx had tweeted Sunday that he wanted to thank Rene Boucher, who was arrested and charged with assaulting Paul in 2017 after getting enraged about yard waste that he alleged was being dumped in his yard near the property line.
"I'll say it again: If I ever meet Rand Paul's neighbor I'm going to hug him and buy him as many drinks as he can consume," Marx said. Boucher is scheduled to be sent to prison for eight months.
He was the first senator known to have contracted the coronavirus when he tested positive in March 2020. Paul told a conservative host on WABC radio in New York on Sunday that he won't change his mind unless "they show me evidence that people who have already had the infection are dying in large numbers or being hospitalized or getting very sick."
"I just made my own personal decision that I'm not getting vaccinated, because I've already had the disease, and I have natural immunity," he said.
The Centers for Disease Control and Prevention recommends that people who have been infected still get vaccinated because experts are not certain how long natural immunity lasts.
CORRECTION (May 25, 2021, 12:25 p.m. ET) A previous version of this article misstated Sen. Rand Paul’s political party. He is a Republican, not a member of the Libertarian Party.