Among the worst impressions the U.S. Securities and Exchange Commission could foster is that it pulls punches on delicate matters involving the rich, powerful and politically connected. Now two Senate committees are investigating whether the commission staff, rather than doggedly pursuing possible insider trading by the hedge fund Pequot Capital Management, held back when it came to taking the testimony of a prominent Wall Street player.  A commission investigator, Gary Aguirre, sought permission from higher-ups to question John Mack, who had briefly worked at Pequot, about his dealings with Pequot's founder, Arthur Samberg. As Walt Bogdanich and Gretchen Morgenson reported in The New York Times on Sunday, the tone of the inquiry shifted drastically once it came to light that Mack was being considered for the job of chief executive at Morgan Stanley.  A supervisor then wrote about Mack's "juice" and "political clout" in internal e-mail messages. Aguirre was not permitted to interview Mack and ultimately was fired - immediately after receiving a merit-based pay raise.  The Senate Finance and Judiciary Committees are pursuing the question of how the Pequot investigation proceeded and why Aguirre was fired. So far, there is hardly enough information available to jump to conclusions about the conduct of Mack or Samberg. The commission has informed both men that it is not seeking enforcement actions against them. What is more important to the public is not the specifics of the case as much as how easily the commission staff can be influenced, whether by reputation, connections or future job prospects.  Senator Charles Grassley, chairman of the Senate Finance Committee, said in a statement that additional questions had arisen because of conflicting statements and documents that had come to light over the course of the Senate panel's inquiry. "My initial concerns haven't been put to rest by what I've learned so far," Grassley said.  Neither have ours. A full airing is in everyone's interest.