Let's be clear. Impeachment is different from the Impeachment Process which has two parts: 1) impeachment by the House of Representtaives for for one or more alledged offenses as determined by the House; 2) trial in the Senate.

President Clinton was impeached for perjury and obstruction of justice.

During any session of Congress (each two years of a Congress is termed a session) there is usually at least one bill of impeachment introduced against a President. Obviously, they are quickly disposed of. The House of Representatives is the sole determinent of an impeacheable offense. Such an alledged offense can be within the meaning of the Constitution's original intent or it can be political. It can be argued that any impeachment includes a political dimension. Certainly, President Andrew Jackson's impeachment was such.