Our challenge today is to explain how Congress evolved into our national nutcase.

I am thinking mainly of the House Republicans. Back in the good old days, last week, these were the guys who said they would vote to raise the debt ceiling only if Obamacare was axed and the Keystone XL pipeline was built.

Ah, last week. Giants strode the earth last week. Last week our nation was governed by men and women who were, as a matter of principle, willing to pay the nation’s creditors when the bills were due just as long as the president canceled his central domestic initiative and oil shippers got a new pipe.

But that was then. This week the House Republican leaders were looking at a long, long list of must-haves that also included changes in regulations relating to coal ash, reduction in Civil Service pensions, restrictions on malpractice suits and an end to some greenhouse gas regulations.

And their members found that list too restrictive. Behind-the-scenes discussion continued about more things the Republicans could demand. A ban on late-term abortions? A trillion-dollar budget cut? Bring back the gold standard? Bring back the bustle? It’s 2013 and anything is possible.

So, what do you think is wrong with these people? Thanks to gerrymandered Congressional districts and the Tea Party, we do seem to have a surprising number of elected officials who actually don’t believe that raising the debt limit so the government can pay its bills is a good plan. (“All that does is just say: ‘Well, you’ve got a little bit more credit — keep spending,’ ” Representative Walter Jones of North Carolina once told a radio interviewer.)But there’s got to be more to it than that. Let’s try to think of three other reasons the United States Congress continues to behave as if it’s playing the Jack Nicholson part in “The Shining.” I’ll go first.

1. The Republicans are desperately, obsessively demonizing Obamacare to cover up the fact that they don’t want to do anything to Medicare or Social Security. Those used to be the party’s obsession — remember privatizing Social Security? But that was before they noticed that the entire Republican base is on Social Security.

Ranting about Obamacare, which one New Hampshire politician recently compared to the Fugitive Slave Act, is an excellent way to give the impression that you’re fighting to reduce entitlements without having to do anything about the actual entitlements.

2. It’s all about Twitter. Social media have transformed Congress’s younger generation. (While much of the Senate is arguably too old to know how to use the TV remote, three of the four leaders of this week’s faux filibuster are 42.) Twitter in particular makes politicians even more self-obsessed than they used to be. “Talking about tomorrow’s #DefundObamacare vote tonight on Hannity. Be sure to tune in!” twittered Senator Ted Cruz on Thursday.

Cruz kept demanding that the Senate “listen to the American people,” but he really meant that they should listen to his Twitter followers. A politician riding on a wave of tweets feels as if the nation is cheering his every word, even when the nation is actually reading the sports page while a select splinter of hard-core supporters manically pound away on their smartphones. A hundred thousand people cheering you on in the social media feels like a mass movement. But this is a gigantic country. You can find 100,000 people who believe in a secret plot by Belgium to corner the market on beetroot.

Richard Baker, the co-author of “The American Senate,” says the late Senator Robert Byrd waged a war against cellphones on the Senate floor: “When he entered the room, there was this whooshing under the desks.” But Byrd is gone, and now we have Ted Cruz.

3. Zombie apocalypse. Only possible explanation.

On Friday, the Senate finally managed to vote to keep the government running until mid-November, when we’d get to do this all over again. It’s now up to the House, which will be having an unusual working weekend while the Republicans decide whether to pass the Senate bill and move on, or festoon it with anti-Obamacare amendments.

The majority whip, Kevin McCarthy, suggested that his colleagues might want to join him for an evening showing of the movie “Prisoners.” One Republican aide worried that the media might read too much into the title, what with the country being held hostage to the House’s current psychosis and all. The media are actually disappointed that McCarthy passed up “Insidious” and “Despicable Me.”Cynics would say that keeping the government going for a few more weeks is just the kind of modest, uncontroversial proposal that automatically vanishes into the black hole that is the current House of Representatives. But maybe there’s hope. After all, on Friday the House members did show they could pass legislation in a purposeful, bipartisan fashion. They approved a bill naming a building in Virginia after a deceased federal worker.