Senate Majority Whip Dick Durbin said on Sunday embattled Sen. Robert Menendez (D-N.J.) should keep his chairmanship of the Foreign Relations Committee despite an investigation into his dealings with a top donor. "Sen. Menendez has given us an assurance that there is no substance to these charges," the Democratic senator from Illinois said on NBC's "Meet the Press." "It's being looked at by the Ethics Committee. Of course, I can't comment beyond that." The Senate Ethics Committee is looking into Menendez's interaction with Salomon Melgen, a Florida eye surgeon who has donated hundreds of thousands of dollars to Menendez and...