When can the president use a pardon during impeachment proceeding?

A president cannot use a pardon to avoid impeachment or influence the impeachment process. The Constitution grants Congress the authority to impeach and remove a president for "high crimes and misdemeanors," and a pardon does not negate or protect against these charges. However, a president may issue pardons for federal offenses after an impeachment has occurred, but such pardons cannot prevent the impeachment itself or shield the president from consequences related to the impeachment process.