The probe addresses unanswered questions about the Uranium One mining company's ties to the Clinton Foundation, the nonprofit founded by the former president, during Hillary Clinton's tenure as secretary of state.

In a 2010 deal approved by a committee including Hillary Clinton and eight other members of President Barack Obama's Cabinet, a Kremlin-connected entity obtained 20 percent of America's uranium production by acquiring Canada-based Uranium One.

Although a joint investigation by the House Permanent Select Committee on Intelligence and the House Oversight and Government Reform Committee is just getting under way, many congressional Republicans already are calling for a special counsel to look into the facts.