The Obama administration has, for the first time, set a goal for Obamacare enrollment: it wants to get 9.1 million people signed up through the exchanges in 2015.

"The number we're going to aim for this year is 9.1 million," Health and Human Services Secretary Sylvia Matthews Burwell said during an event at the Center for American Progress Monday.

There are two things significant about Burwell's statement. First, the fact that the White House set a goal is a notable. The Obama administration has typically eschewed goal setting. During the 2014 open enrollment season, officials were quick to point out that the Congressional Budget Office's projection of 7 million sign ups in 2014 was just that — a projection, but definitely not a target. It was simply what forecasters thought would happen.

That the administration is drawing a line in the sand — saying, this is what we want to achieve in the second open enrollment period — suggests they're pretty confident that the target is one that they can meet.

The second important thing to know about the 9.1 million target is that it is way lower than Congressional Budget Office projections. The CBO has previously projected that 13 million people would enroll through the exchanges in 2015. The White House's goal is about 30 percent lower.

the white house goal is 30 percent lower than cbo projections

A new Obama administration report, which explains the thinking behind the 9.1 million goal, grapples a bit with this pretty significant difference. It argues that the CBO projections assume a higher rate of employers dumping workers onto the exchange than has actually occurred.

Recent data suggest mixed evidence about the extent to which there is a shift in ESI [employer-sponsored insurance] and off-Marketplace individual coverage into the Marketplace," the report argues. "Thus, there is considerable uncertainty that a large shift will occur in the next two years."

The report also cites the case of other new insurance programs, like the Children's Health Insurance Program and Medicare Part D, that suggests it takes about four to five years for coverage to grow to its stable, final level. CBO currently has Obamacare hitting its projected, stable enrollment (25 million) over the course of three years.

The White House is now saying it thinks the 25 million target is attainable, but over a longer time frame — and setting a lower, easier enrollment target for 2015 as a result.