There's a fun new meta-debate over insider-trading, beyond the not-so-simple question of what is and isn't.

Federal investigators interviewed a Senate staff member for four hours Thursday, part of a wide-ranging insider-trading probe into how a major change in U.S. health-care policy leaked to Wall Street traders before it was announced.

But Thursday's interview with Rodney Whitlock, a health-care aide to Sen. Charles Grassley (R., Iowa), took place only after delays over the terms of the questioning, according to people familiar with the matter. In addition, Mr. Whitlock didn't answer several questions from investigators that touched on a parallel investigation by Mr. Grassley's staff, according to a written statement from Mr. Grassley's office.

At issue is the constitutional privilege held by members of Congress and their staff to protect them from certain civil and criminal lawsuits. Attorneys for the Senate and the staffers have said formal interviews can proceed only without waiving the provision in question, known as the Speech or Debate Clause….

Speech or Debate Clause issues have thrown an unexpected wrinkle into one of the biggest recent insider-trading cases in Washington. The speech-or-debate privilege doesn't exempt crimes, such as bribery, committed while engaging in legislative acts, but it could pose significant legal hurdles the Justice Department must overcome before it obtains evidence and testimony from Congress.

If the testimony is needed in court proceedings, the full Senate might have to vote to give approval. The protections extend to former lawmakers and aides when it involves activity that occurred during their time in Congress.

Insider Probe Caught in Knot [WSJ]