When a suspicious package filled with white powder showed up at his house in Kentucky on Monday, Sen. Rand Paul, R-Ky., said he knew exactly who was to blame for inspiring the threat: Pop singer Richard Marx.

Paul pointed to a Sunday tweet in which the singer behind hits like "Don't Mean Nothing" and "Endless Summer Nights" said he would buy drinks for Paul's neighbor, who broke several of the senator's ribs in a 2017 scuffle. The intent, Paul argued, was to incite another violent attack against him.

"As a repeated target of violence, it is reprehensible that Twitter allows C-list celebrities to encourage violence against me and my family," Paul said in a statement shared with Politico, which broke the news of the suspicious package. "Just this weekend Richard Marx called for violence against me and now we receive this powder filled letter."

Marx, who often tweets about politics to his more than 300,000 followers, countered that his tweet was simply "a wise-crack about Rand Paul's neighbor."

"I'm the only person on Twitter who's ever referenced Rand Paul's neighbor," Marx sarcastically replied to one critic sharing Paul's accusations on Twitter. "Must have been me."

The incident has become the latest rallying cry for conservatives who claim that social media platforms overtly target right-wing actors. It comes as Paul has faced blowback this week for saying that he will refuse the coronavirus vaccine, citing the antibodies he says he has from contracting covid-19 last year.

On Monday, a package arrived at Paul's house illustrated with an image of the senator in a neck brace and with a cast on his arm, Fox News reported, above text reading, "I'll finish what your neighbor started."

In 2017, Rene Boucher made a "running tackle" on Paul after an argument over yard waste from the neighboring homes, breaking six of Paul's ribs. Boucher later pleaded guilty to federal charges of assaulting a member of Congress and was sentenced to 30 days in prison.

In 2018, Paul was again the target of a violent threat. U.S. Capitol Police arrested a man who Paul said had called one of his Kentucky offices and "threatened to kill me and chop up my family with an ax."

Now the FBI's Louisville office is working with the Warren County Sheriff's Office to investigate the package at Paul's house, the agency told the Louisville Courier-Journal. The Capitol Police have also opened a probe, Politico reported.

Marx, who rose to fame in the late '80s and then recorded numerous top 20 hits in the '90s, has grown his online profile during the pandemic with podcasts and a prolific, conservative-baiting Twitter feed that one newspaper critic called "hilariously profane."

On Sunday, after Paul drew headlines by saying on a podcast that he planned to skip the vaccine, Marx lashed out at the Republican lawmaker.

"I'll say it again," Marx tweeted. "If I ever meet Rand Paul's neighbor I'm going to hug him and buy him as many drinks as he can consume."

As backlash grew early on Tuesday over Paul's statement, Marx responded by tweeting out a story on the senator contracting covid-19 last year and potentially exposing other lawmakers.

"You know who actually put multiple people's lives at potential risk?" he wrote.