Washington DC - A woman who sent an envelope containing the poison ricin to then-President Donald Trump has been sentenced to almost 22 years in prison, and said she only regrets that she "couldn’t stop Trump."

Pascale Ferrier will remain under judicial supervision even after her release, the US Department of Justice announced on Thursday.

The now 56-year-old, with Canadian and French citizenship, admitted to manufacturing ricin in her Quebec home in September 2020.

She then sent letters containing the poison to the White House and to eight law enforcement officials in Texas.

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According to the Department of Justice, the woman had spent several weeks in detention in Texas in 2019 and blamed law enforcement officials.

She had also railed against Trump on social media. In the letter to the then president sent in September 2020, she had asked the Republican to withdraw his candidacy for the 2020 presidential election.

"I found a new name for you: 'The Ugly Tyrant Clown,'" she reportedly wrote. "You ruin USA and lead them to disaster. I have US cousins, then I don’t want the next 4 years with you as President. Give up and remove your application for this election!"

The envelope to Trump was intercepted by the secret service.

The lengthy prison sentence is part of an agreement with the prosecution which a court has now rubber-stamped. Ferrier will be deported from the US after she finishes her jail time.

"I consider myself to be an activist, not a terrorist," Ferrier said at her hearing on Thursday, calling herself a "peaceful person." "Activists are constructive, terrorists are destructive."

"The only regret I have is that it didn’t work and that I couldn’t stop Trump," she added.

Letters laced with the highly toxic ricin were also sent to then-president Barack Obama and then-New York mayor Michael Bloomberg in 2013.

Ricin is made from material left over from castor beans processing, and can be lethal even in small quantities.