David Bransfield, a state outreach coordinator for Young Invincibles, a group which supports President Barack Obama's health care law, talks with student Philippe Komongnan, 27, who is in the process of signing up for health care, at the University of the District of Columbia in Washington, Thursday, Jan. 30, 2014. An army of workers and volunteers has fanned out around the country trying to enroll young and healthy people in health insurance now available through Obamaís signature law.

WASHINGTON — “Do you guys have health insurance?” David Bransfield asks each time a group of backpack-toting college students passes by.

Some nod yes. A few promise to stop back after class. Others don’t bother removing their headphones.

Nearly every day, Bransfield comes to a satellite campus of the University of the District of Columbia in the shadow of the U.S. Capitol, sitting for hours behind a table in the lobby of a classroom building. Armed with an Apple laptop and a pile of fliers, he’s part of the army of workers and volunteers fanned out around the country trying to enroll young — and probably healthy — people in health insurance available through President Barack Obama’s signature law.

Run largely by groups with close ties to the White House, the on-the-ground recruiting effort is based in part on lessons learned from Obama’s two presidential bids, which revolutionized the way campaigns tracked and targeted voters.

“On the campaign, you want to be able to find an Obama voter and you want to get them to vote,” said Matt Saniie, who worked on the 2012 campaign’s data team and is now analytics director at the organization Enroll America. “In the enrollment world, you want to find someone who is uninsured and you want to get them to enroll.”

More than any other group, participation from the so-called young invincibles — people ages 18-34 — will be crucial to the health law’s success. The Kaiser Family Foundation estimates that about 40 percent of those who enroll need to be young and healthy to balance out the higher costs of insuring older, sicker people.

But less than two months before the March 31 sign-up deadline, the administration is lagging behind its goal. Young adults made up about one-fourth of the 2.2 million people who enrolled in the exchanges through December, the last time the administration released demographic data. Officials announced in mid-January that a total of 3 million people had enrolled in insurance plans, but they didn’t update the demographic details.