At what point do we decide that a political system has become decadent?

The breaking point for me was the Anthony Weiner story, not just or even primarily for what he did but because it came at the end of what old Thomas Jefferson might call “a long train of abuses.” You really do wonder what’s happening to our democracy and those who serve it.

The Weiner circus is bad enough. Social networking has taken us where human nature always threatens to go: downward. Do we want to give politicians incentives to limit their thinking to 140 characters? Will Weiner’s experience — and former congressman Chris Lee’s adventures on Craigslist — encourage politicians to question whether constituents want anything close to the level of detail about their lives that fans expect from pop stars and marquee athletes?

Weiner’s self-destruction is a terrible blow for cable television bookers and will create a certain sadness among liberals who are short of troops willing to take it to the other side from one five-minute news cycle to the next. And let’s simply stipulate that all the negative adjectives being thrown Weiner’s way are justified.

What’s amazing is that the Scandal Management Handbook, 36th edition, offered him the perfect way out. When caught, fess up immediately, declare right from the start that you are a victim of a terrible addiction, go into treatment and disappear for a while.

You are rarely challenged these days when you take a loss of virtue and turn it into a medical condition. And you avoid the problem of encouraging your allies to defend you on a matter about which you know you are guilty. Weiner’s congressional colleagues are reluctant to defend him because they accepted his denial and feel badly burned.

Now, I am always wary of those who do what I’m about to do next: Take a tawdry sex scandal that people read about because we like to read about tawdry sex scandals, and use it to make some larger point.

But the Weiner episode marked the culmination of several months during which other sideshows involving outrageous male behavior — John Ensign and John Edwards come to mind — dominated news coverage at a moment when our country’s future really is on the line. (Bill Clinton’s scandal played out when we were in very good shape, which is one reason he survived.)

Add to this the political media’s tendency to prefer covering personalities that the media created in the first place (Sarah Palin and Donald Trump, above all) to those taking the trouble of running for president and thinking through what they want to say. It’s another case of politicians being reduced (or, maybe, reducing themselves) to celebrities.

I have no particular sympathy for the political views of Mitt Romney, Tim Pawlenty or Rick Santorum, but at least the three of them are doing the hard work that democratic politics requires. Thus: Palin’s unusual comments about Paul Revere got far more attention than did Pawlenty’s economic speech this week. It fell to policy bloggers such as The Post’s Ezra Klein to take Pawlenty’s ideas apart. Thus: Palin’s bus trip to the New Hampshire seacoast got at least as much attention as Romney’s announcement of a real, live candidacy.

But it’s not all the media’s fault, and this is not just about politicians who conduct themselves badly in their personal lives. Much of what passes for debate consists of irritable ideological gestures. The recent disappointing economic news has not changed the set-piece Washington deficit debate one bit.

Big numbers are thrown around — Sen. Jon Kyl said Tuesday that Republican agreement to raising the debt ceiling would require $2.5 trillion in spending cuts — with little inquiry as to how such reductions would affect actual people, future economic growth or our capacity to invest in ourselves. Ah, but trying to answer such questions would distract us from the Weiner story.

Okay, most of us will always pay attention to sex stories, and apocalyptic fears are usually a form of paranoia. But we’re a superpower with big economic problems. We’re acting like a country that has all the time in the world to dance around our troubles by indulging in ideological fantasies and focusing on the behavioral fantasies of wayward politicians — who, by the way, keep creating opportunities for distraction.

Britney Spears, appropriately enough I suppose, has a catchy song out with the refrain “Keep on dancin’ till the world ends.” Forgive me for wondering whether her song will provide the soundtrack for some future documentary on our national decline if we don’t get very serious, very soon.