A cloud of scandalous allegations is rapidly growing over Sen. Robert Menendez (D-N.J.), putting Democratic leaders in a difficult position as the integrity of their immigration point man in the Senate falls under question at a critical time. The bad news keeps coming: a Senate Ethics probe, allegations involving underage prostitutes, an FBI investigation of a key campaign donor, undisclosed flights on the donor’s private plane, and now, reports linking Menendez to a multi-million dollar contract he helped obtain for the disgraced donor. Menendez denies nearly all of it. But it couldn’t come at a worse time for the new...