The March 31 deadline maneuver

One is that the administration fears the system will crash under the kind of demand spike they saw in the last weeks of December enrollment. This is just a prophylactic measure designed to make sure that people who genuinely tried to sign up but couldn't get through don't get hit by the individual mandate — and show up on television, crying, shortly thereafter.

The second is that the administration knows, or strongly suspects, that most of the people who have so far bought insurance are people who already had insurance. They're concerned that when enrollment is closed, they're only going to be able to point to a net reduction of a few million uninsured – - and that almost all the reduction will come from people on Medicaid. So they're hoping to get a few hundred thousand or million more uninsured people to sign up during the grace period.

The third, most worrying, possibility is that the demographics haven't really improved substantially. A lot of commentators, including me, have been expecting the "Young Invincibles" — the younger, healthier customers whose premiums will subsidize care for the previously uninsurable — to show up on the exchanges this month. So far, only 25 percent of total signups have come from young adults. And even that may overstate things, because it isn't unreasonable to assume that the folks who selected plans but didn't pay for them are young and irresponsible people like … well, like me at 25.

Before the exchanges opened, the administration said it needed 40 percent of enrollments to come from young people to keep the prices of exchanges policies from spiking. The improbable worst-case scenario sketched by a December report from the Kaiser Family Foundation was 25 percent. Yet that's where we've been stuck for months.

You can argue (as that report does) that age itself doesn't matter much. But it seems unlikely that age is the only problem; if young people are staying away from the exchanges in droves, it seems likely that we're also seeing quite a bit of what insurance experts call "adverse selection": The folks who are buying insurance are disproportionately the ones who expect to need some costly health care in the coming year. If that's the case, expect premiums to rise sharply — which is just what insurers have been threatening.

So again, here's the really worrying scenario: The demographics haven't budged, or have only barely improved from earlier months. The White House knows that means that big premium increases are in the offing for 2015, and they're hoping to head them off at least temporarily with this delay.

Extending open enrollment, which is essentially what they're doing, would then be a desperate play to get more young, healthy customers into the exchanges, and perhaps to make it a bit harder for insurers to raise rates. In some states, insurers have to file preliminary rate increases in May. And thanks to this latest extension, they won't have final data to back up any requests for a premium hike.

Those are the explanations I can think of for the administration's somewhat inexplicable move. Which is the most likely?

On that, your guess is as good as mine. Eventually, the data will be released and we'll know more. But to really understand what they were thinking, we may have to wait until some enterprising journalist writes the definitive history of Obamacare.

See also:

• How high will 2015 health premiums go?
• Unions: Under the Obamacare bus?
• Bad state Obamacare sites