The impeachment provisions of the Constitution were designed to protect the government and the nation from "high crimes and misdemeanors." Thankfully, in 1974, there was a Democratic Congress with enough spine to take on a President who was truly guilty of such offenses, by obstructing justice in the investigation of an effort to hijack the 1972 Presidential election.
But to the Republicans, the only such offense truly justifying impeachment is the existence of a Democratic President. The existence of a second-term Clinton Presidency, and the desire to achieve payback for Nixon's impeachment, led them to pursue Clinton's impeachment over charges that did not even begin to rise to a Constitutional level. This process nearly cost the GOP its House majority in 1998, but it was politically successful in other ways. It lead a sufficiently bullied President to spend the final two years of his Administration largely caving to Republican demands, including the repeal of the Glass-Steagal Act.
Which is probably why they may be thinking about a rerun if Obama wins in 2012. Of course, the success of such a strategy largely depends on two things: whether they control Congress, and whether Americans think rolling back the Bush tax cuts is an impeachable offense. Neither of those propositions in guaranteed.
But Norquist's willingness to float this idea says as much about the political and intellectual bankruptcy of the modern GOP. Shame on the majority of us if we give in to it.