A federal grand jury in Miami is investigating Sen. Robert Menendez (D-N.J.), examining his role in advocating for the business interests of a wealthy donor and friend, according to three people aware of the probe.

Menendez has intervened in matters affecting the financial interests of Florida ophthalmologist Salomon Melgen, seeking to apply pressure on the Dominican government to honor a contract with Melgen’s port-security company, documents and interviews show. Also, Menendez’s office has acknowledged he interceded with federal health-care officials after they said that Melgen had overbilled the U.S. government for care at his clinic.

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