The question of the hour is: What do the words "high Crimes and Misdemeanors" mean? I like your initial answer, but I have a few additions by way of friendly amendment.
Like you, I begin by rejecting the cynical view that these words mean anything clever politicians want them to mean. Clinton's critics cannot honorably condemn him for twisting words unless they show that they take words seriously.
But the words "high Crimes and Misdemeanors" do not exist in isolation. They are part of a larger constitutional phrase, which in turn is part of a larger constitutional framework. Begin with the phrase as a whole: "Treason, Bribery, or other high Crimes and Misdemeanors." If we want to get a sense of how "high" misconduct must be to be impeachable, we should start with the two textual examples of treason and bribery. These are "high" crimes indeed. Treason involves betraying America to a foreign power, and bribery involves official corruption of the worst kind. (And in the case of a president who bribes people to vote for him, the bribery calls into question the very legitimacy of his election in the first place.) Few crimes are as "high"--as deadly to the Republic--as treason and bribery.
The next step you take is elegant and powerful--contrasting the Impeachment Clause language with two other constitutional phrases that encompass garden-variety crimes. All three phrases include the word "treason," but neither of the other phrases is limited to "high" misconduct. This elegant linguistic contrast proves that not all criminal conduct is "high" enough to be impeachable. When the framers wanted to speak of all crimes, high and low, they knew the words, but they consciously limited impeachment to a more narrow category of criminal offenses. (Conversely, not all impeachable misconduct need be technically criminal--but that is another story.)
Comparing and contrasting phrases in the Constitution is one way to take seriously the document a whole, but there is at least one other classic method--what Charles Black called structural argument, aimed at deducing the basic architecture of the Constitution. And this kind of argument adds an important new insight: In thinking about impeachment, we should sharply distinguish between presidential impeachment on the one hand and impeachment of federal judges and Cabinet officers on the other. If we look narrowly at the impeachment clause in isolation, we may miss this important truth. After all, the same linguistic standard for impeachment is laid down for presidents and nonpresidents alike. But this standard must be read alongside other parts of the Constitution that do sharply distinguish between presidents and nonpresidents.
An analogy: The phrase "advice and consent" is the same for Cabinet officers and Supreme Court justices. In both cases the president nominates, and the Senate then decides whether to confirm--to give its "advice and consent" to the nomination. But the Senate has long understood that these words mean one thing when it comes to Cabinet officers and something different when it comes to justices. Cabinet members are part of the president's executive branch team. They will leave when he leaves, and they take their orders from him--and so the Senate rightly gives the president great deference in picking his own underlings. Supreme Court justices are not part of the president's team; they are not even part of his branch (the executive). They do not take orders from him and will not leave when he leaves. They should be independent of him--and so the Senate rightly gives the president less deference when he nominates justices. Thus sometimes a single phrase in the Constitution sensibly applies differently when it interacts with different parts of the Constitution.
Here are a few structural reasons for treating presidential impeachments more cautiously than impeachments of Cabinet officers and judges. First, there is only one president, in whom the Constitution vests all executive power. To remove him is to wholly restructure an entire branch of government. Second, and related, to do so is to put the nation--perhaps the world--through severe trauma, unlike an impeachment of any other officer. Third, to remove a president is to undo the votes of millions of Americans--again unlike any other impeachment (with the possible exception of the vice president). Fourth, for the legislature to undo the verdict of the people in the absence of the most compelling of reasons is to risk sliding into a kind of parliamentary democracy that our Constitution was designed to reject. When senators remove a judge or justice, they unelect an officer that they themselves in effect elected. But when senators remove a president, they unelect an officer that the people (via the Electoral College) elected. Fifth, the job descriptions of various offices differ, and so what counts as disqualifying conduct should also differ. For example, overt partisanship in office is inconsistent with the job description of a modern judge but not of a modern president. And if we insist on locating specific words in the Constitution confirming our structural intuitions, note that only in presidential impeachments does the chief justice preside. There are several good reasons for this, and one is to provide a special measure of solemnity, reminding us that presidential impeachments are unique.
If we look beyond the words of the Constitution and its overarching structures to the Constitution in practice over two centuries, we see confirmation of my main point. Only twice before has the House seriously pondered presidential impeachments, and in both cases the president had a suspect electoral mandate. The American people never voted for Andrew Johnson as president in the 1860s--they voted for Lincoln, and Johnson was in fact undoing much of what Lincoln had stood for. (A similar objection had been raised a generation earlier against John Tyler, who became president when William Henry Harrison died, and whose antics in office generated impeachment talk.) And although the people did vote for Richard Nixon in 1972, his election crimes and unprecedented dirty tricks campaign against the opposition party made it awkward to argue that he had been elected fair and square.
And so my bottom line is this: However "high" we think misconduct must be to be impeachable, we should be especially wary of lowering the bar in the case of duly elected presidents.