FALLS CHURCH, Va. — Sandwiched between two doctors’ offices at a roadside plaza here is the headquarters of a small team of veteran Republican investigators, operating almost as a private detective squad, who since late last year have had a determined goal: bringing down Senator Robert Menendez, Democrat of New Jersey.

“We’ve never sent a Democrat to jail,” said Ken Boehm, the chairman of the group, the National Legal and Policy Center, as he looked up from a table filled with his Menendez files and engaged in what was to him a bit of wishful thinking.

To Mr. Menendez and his staff, the work going on at this suburban Washington office suite, paid for by donations from prominent Republicans nationwide, is proof that the still-building news media frenzy focusing on his actions to help a Florida eye doctor is at least in part a political smear.