BOSTON (AP) — A Massachusetts man is set to plead guilty to sending threatening letters with white powder to President Donald Trump’s sons and others.

Daniel Frisiello is expected to plead guilty in Boston’s federal court on Wednesday.

The letter to Donald Trump Jr. was opened in February by his now-estranged wife, Vanessa Trump, who reported she was coughing and felt nauseous and was briefly hospitalized. The substance turned out to be nonhazardous.

Authorities said other recipients of Frisiello’s threatening letters included Eric Trump, Democratic U.S. Senator Debbie Stabenow of Michigan and Michele Dauber, a Stanford University law professor who has promoted the effort to recall California judge Aaron Persky.

Frisiello’s attorney has said he has some “issues” and has been on medication his entire life.