Legally, impeachment, which is like an indictment, requires serious wrongdoing in order to be invoked—“Treason, Bribery, or other High Crimes and Misdemeanors,” according to the Constitution. Peterson, the University of Utah law professor, argues that fraud and racketeering fit the bill, and both are at play with Trump University. But the decision is mostly political. That means relatively trivial offenses (perjury regarding extramarital relations, as with Clinton) can get blown up, while serious ones (use of torture in detention, as with George W. Bush) can get ignored. The political will to unseat a president must be overwhelming for things to go anywhere, and the fiasco of Clinton’s impeachment trial, which saw Republicans lose seats in Congress, lessened everyone’s appetite for more of the same.
Source: Will Trump Be Impeached? | Vanity Fair