I. The first several paragraphs of this lengthy disquisition, providing some etymology and colonial American background on high crimes and misdemeanors, argue that the Founders left the phrase grave but broad intentionally. The phrase was intended to be a real check on the powers of the Executive, without being so elastic as to give Congress a parliamentary ability to remove a president at any time for narrow political motives. This general characterization is valid as far as it goes.
Note, however, that this article, written with William J. Clinton in mind, emphasizes offenses besides treason or bribery, since the GOP Congress was not accusing him of those. George W. Bush may not be limited to the purview of the high crimes and misdemeanors phrase. Taking the least of the offenses first