Even as the House Judiciary Committee prepares to decide whether or not to proceed with an inquiry, for many people in the U.S. the impeachment of President Clinton remains the unthinkable. Kenneth T. Mayland, senior vice president and chief economist at KeyCorp, a Cleveland-based financial services company, has thought about the economic impact of presidential impeachment, conviction, and removal from office. And he concludes there wouldn't be a heavy hit. Investors have been drawing their own conclusions for several months and adjusting their portfolios; whatever the outcome, by the time there is one, the result will have been somewhat discounted, Mayland asserts in the current KeyViewpoint newsletter. "Perhaps the worst thing that could happen is if this thing drags on for a long time. . . . It will be tough for government to get much done as long as a cloud of uncertainty hangs over it."