The House Intelligence Committee earlier this month issued a subpoena to the bank used by Fusion GPS in hopes of finding out who paid the opposition research firm to produce the infamous dossier of research on Donald Trump, according to a source familiar with the situation.

The subpoena of TD Bank was issued on Oct. 4, the same day that the committee subpoenaed documents and interviews from Fusion’s three co-founders, Glenn Simpson, Peter Fritsch and Thomas Catan.

Fritsch and Catan invoked their Fifth Amendment rights during a short interview before the committee on Wednesday.

The Washington Examiner first reported the news of the bank subpoena on Friday.

TheDC is told that the House committee, which is investigating Russian interference in the presidential campaign, wants “to know what [Fusion’s] hiding” regarding its clients.

Fusion, which operates in Washington, D.C., hired former British spy Christopher Steele last June to investigate Trump’s personal and business activities in Russia. But Fusion’s clients remain a mystery. According to various news reports, Fusion was first hired in September 2015 by a Republican donor who opposed Trump. After Trump ascended to the GOP nomination, that donor dropped from the Trump investigation, and Fusion found a Clinton supporter to continue paying for its probe.

Fusion has refused to identify its clients, citing confidentiality agreements. In August, Simpson, the Fusion co-founder who oversaw the dossier project, was interviewed by the Senate Judiciary Committee for 10 hours. His attorney released a statement following the interview saying that he did not reveal the names of Fusion’s clients.

According to the Examiner, Fusion GPS is asking a federal judge in Washington, D.C. to block the subpoena for the TD Bank records.

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