Now that Obamacare has finished with an amazing surge in signups, apparently passing the 7 million mark for the exchanges, there have been two main responses. Republicans are in full-on denial — the books are cooked! Nobody has paid! It’s only because people have been forced to do it! Benghazi! Vince Foster! Meanwhile, progressives are full of caution. It’s just a start, we don’t know how well this will work in the longer run, too soon to celebrate.

The right-wing reaction is, of course, ludicrous. But the cautious progressives are being too cautious. This really is what Joe Biden would have called a Big Frothing Deal, or something like that.

The key question you need to ask is, what would make Obamacare fail if it did fail?

Contrary to what the right has been saying, there’s nothing at all wrong with the concept of a government guarantee of health insurance — every other advanced country does it, and they all have much cheaper care than we do. The question, instead, was whether the compromises made to get past the political barriers to universal insurance had produced a system too complex to work.

I’ve always thought of Obamacare as a sort of Rube Goldberg device that awkwardly simulates the results of a single-payer system. It’s run through private insurance companies in part to buy off the industry, in part to let most people with good insurance keep it. It relies on a mandate plus subsidies, rather than full funding via the tax system, in part to keep down the headline spending number. And so on. The resulting system isn’t what anyone would design from scratch; it was, however, probably the only kind of system we could get.

So, the risk was that it would be too Rube Goldbergy — that it would be too hard to get the system up and running, that people wouldn’t hear about their options or be able to navigate their way through the choices available. And for a while, with the botched website, it looked as if this worst-case scenario was coming true.

But now we know: despite the initial botch, despite difficulty getting the word out to Latinos and others, we have a lot of people signing up. And that was the hard part. When the next signup window opens, even more of the bugs will have been worked out, and many people who didn’t sign up for 2014 will be hearing word-of-mouth stories about the benefits.

We’ve had proof of concept, and that means we’re over the hump. This was a very big day.