Sen. Ben Cardin (D., Md.) is seen as next in line to replace Sen. Robert Menendez (D., N.J.) as chairman of the Senate Foreign Relations Committee if the New Jersey Democrat is forced to resign.
Menendez is currently being investigated by the Senate Ethics Committee over his relationship with Dr. Salomon Melgen, a major Democratic donor whose South Florida office was raided by federal agents earlier this week.
Cardin is the next most senior Democrats on the committee, after Sen. Barbara Boxer (D., Calif.). Sources believe Boxer would be unlikely to give up her conflicting chairmanship of the Committee on Environment and Public Works.
Cardin joined the committee after winning his Senate seat in 2006, and previously served in the House for 20 years.
He would have to resign his position co-chairing the less-powerful Commission on Security and Cooperation in Europe, also known as the Helsinki Commission.
If Cardin declines to do this, the baton would likely be passed to Sen. Bob Casey (D., Pa.), who also joined the Foreign Relations Committee in 2007 but has less seniority than Cardin. Casey holds no other chairmanships.
Cardin’s office declined to say whether the senator would consider stepping down from his leadership on the Helsinki Commission to take on the Foreign Relations Committee chairmanship, in the case of Menendez’s resignation.
"We certainly are not speculating on anything like that," said his spokesperson Susan Sullam.
Both Cardin and Casey are considered to be within the Senate mainstream on foreign policy. Cardin was a driver behind the Magnitsky Act and is known as a fairly active voice on human rights issues.
Cardin has also expressed concern over defense secretary nominee Chuck Hagel’s positions on Iran. Casey recently gave a speech at the Foundation for Defense of Democracies calling for a "more robust U.S. response to the crisis in Syria."
Menendez will officially assume chairmanship of the Senate Foreign Relations Committee when John Kerry exits the Senate today.
The New Jersey Democrat, who has been a leading advocate on Iran sanctions, has been accused of accepting free plane trips for campaign business and failing to pay the agreed-upon wages to underage prostitutes. His office denies the charges.