“Don’t stop thinking about tomorrow,” commands the relentlessly chirpy Fleetwood Mac tune that served as Bill Clinton’s 1992 campaign theme.

But last week, in an exclusive article for Vanity Fair, “that woman,”Monica Lewinsky, forced Bill, Hill and the rest of us to take a look back.

Lewinsky, now 40, is someone who definitely didn’t “love the ‘90s.” “The Clinton administration, the special prosecutor’s minions, the political operatives on both sides of the aisle” and the emerging new media turned Lewinsky’s youthful indiscretion into a life-wrecking mistake, making her the permanent punchline to a dirty joke.

It seemed like great fun at the time, I’m embarrassed now to admit, digging through the Starr Report and cackling over the naughtiest footnotes. With the benefit of 15 years of mature hindsight, what should we make of the Clinton impeachment imbroglio?

Clinton figured out what he thinks long ago: he’s the hero of this sordid little drama. “I am proud of what we did [on impeachment]” he proclaimed in April 2000: “I think we saved the Constitution of the United States.”

To borrow George Will’s signature line: Well.

Clinton saved something, alright, but the national charter isn’t the first thing that comes to mind. Still, there is a constitutional lesson we can draw from the Clinton impeachment: Our system makes it far too hard to remove a president.

In an important new book, The Once and Future King: The Rise of Crown Government in America, legal scholar F.H. Buckley argues that our presidential system of government lacks important “safety valves” present in parliamentary regimes. The president’s fixed term makes it nearly impossible to remove him. We manage fewer than one presidential impeachment per century, and in 225 years, the Senate has never successfully removed one. In contrast, “prime ministers may be removed at any time when Parliament is in session through a nonconfidence motion”; weak leaders can even be dumped by their own party without bringing down the government.

“Impeachment, observed Jefferson in his old age, was not even a scarecrow,” Buckley writes; if anything it’s an even weaker check today.

In the view of the impeachment clause that currently dominates the legal academy, there’s essentially no way to remove a president for misbehavior, neglect or incompetence. During the Clinton imbroglio, scads of concerned law professors dutifully advanced an interpretation of “high Crimes and Misdemeanors” lenient enough to let Bill skate. They drew a line between “public” and “private”: Abuse and corruption related to the exercise of presidential power are impeachable; private misdeeds (like perjury and obstruction of justice to cover up an affair) are not. The always-reliable Cass Sunstein provided the unintentional reductio ad absurdum to this line of reasoning, arguing in the University of Pennsylvania Law Review that if the president were to up and “murder someone simply because he does not like him,” it would make for a “hard case.”

But as law professor Sanford Levinson puts it, “Why in the world should ‘We the People’ not be able to break the lease and evict a manifestly unsuitable or incompetent president and replace him with someone presumably more able?”

Levinson favors a constitutional amendment allowing a congressional “no confidence” vote and removal of the president. Adding that “safety valve” to the Constitution would be a longshot, to say the least.

But years ago, we went through a yearlong constitutional conniption because the Constitution makes it so absurdly difficult to dethrone a misbehaving executive. Given the vast powers the modern president wields, it ought to be easier to “throw the bum out.”