56. Which institution(s) is responsible for examining financial reports and/or investigating violations?

Paragraph 437d - Powers of the Commission.

United State Code, Title 2, The Congress. 

Jurisdiction over the Federal Election Campaign Act (FECA) is shared by two components of the United States Government: the Federal Election Commission and the United States Department of Justice. The FEC has exclusive civil jurisdiction over all violations of the FECA, including those committed negligently or knowingly and wilfully. The Department of Justice has exclusive jurisdiction over all FECA crimes, that is, violations that are committed with criminal intent and involve USD 2,000 or more in a calendar year.

GRECO (2011), Evaluation Report on the United States of America Transparency of Party Funding (Theme II), p.21.