Who are those people standing behind Obama?

Shortly after noon last Monday, 17 smartly dressed Americans filed onto risers at the rear of the East Room of the White House. Their job, for the next 15 minutes or so, was to stand and gaze attentively at President Obama’s back.

Obama, like most presidents in the age of television, often gives speeches against a human backdrop. The people who join him onstage aren’t just a collection of regular folks, even when they’re billed as such: They’re carefully sourced, selected, and positioned by the White House for maximum messaging impact.

Take some of the president’s recent speeches. In April, Obama gave a speech on raising taxes on millionaires and was surrounded by wealthy people who want their taxes raised. In June, he gave a speech on keeping student-loan interest rates low and was surrounded by college kids. On Monday, he gave a speech on keeping middle-class taxes low and was surrounded by middle-class taxpayers.

To find human props, the White House reaches out to local and national groups who care about the relevant issue, according to the White House and others familiar with the process. Social media, past contacts, and personal connections also help the White House find attendees.

It’s usually fairly easy to grow an audience, even on short notice. “This is precious real estate for organizations who are trying to get their message out—and also great honor,” said Josh King, a former director of production for presidential events under President Clinton.

“We often reach out to members to have them participate in rallies, policy announcements, or other events with the president and vice president,” said a source close to labor. The Center for American Progress’s student arm, Campus Progress, has helped gather college students for student-centered events in the past.

The White House carefully selects and positions the people standing onstage with the president. This administration and previous administrations typically pick a group that’s diverse by ethnicity, age, and gender, King said. Sometimes the communications team will make wardrobe suggestions, like encouraging law-enforcement officials to show up in uniform.

“It’s something that all administrations do,” Martha Joynt Kumar, professor of political science at Towson University, said of the careful staging. “Why waste an event just on sound? The picture is important as well.”

The advocacy group Doctors for America helped organize one of the most memorable events of Obama’s tenure: an audience of white-coated doctors that packed the Rose Garden for a 2009 speech on health care reform. Most doctors wore their own coats to the event, according to organizers, but extra coats were distributed to make sure every attendee had one on.

Dr. Mona Mangat, an allergy specialist from Florida, was among the physicians Doctors for America called. “I was obviously very excited, but it sort of came out of nowhere,” Mangat said of her invitation to the Rose Garden. It was also nerve-wracking to hear, a few days later, that she’d been selected to stand beside the president as he delivered his remarks.

Mangat was one of two Doctors for America members who took the stage with Obama that day. The other, Dr. Hershey Garner, hailed from Arkansas. Also flanking the president were Dr. Richard A. Evans, one of Maine’s two delegates to the American Medical Association, and Dr. Amanda McKinney, a doctor from Nebraska. McKinney, Mangat remembers, was a friend of a White House staffer.

Social media has given a new dimension to White House stagecraft, helping the president’s team both find audiences and hone speeches. Last winter, the White House invited Americans to share personal anecdotes about what an extra $40 in their paychecks would mean to them. The call for personal stories—many of which were submitted online, or posted on Twitter—provided fodder for a February speech on extending the payroll-tax cut.

“I want to thank you for helping to tell your story, and tell the story of why this is so important,” Obama said, surrounded by Americans who had answered the $40 question. “And I just want everybody, all across the country, to keep the pressure so that we get this done.”

At last week’s event on tax rates, the interaction between the president and the crowd on the risers was minimal. Obama walked straight to the podium and started to speak. He identified “these good-looking people behind me” as people who could see their taxes go up at the end of the year, but didn’t otherwise refer to them or their stories.

Even so, the White House created a politically meaningful visual. “If you look at the ‘tight shot,’ that key box around the president's head that videographers zoom in on during the bulk of the speech, all of the six people who immediately envelop the president are women,” King wrote in an e-mail. Women, King noted, are a key demographic group for the president.

The world doesn’t usually learn much about the people who stand behind the president, unless they’re given a speaking role or are named by the White House. For Mangat, being named by the White House and meeting the president have helped her raise her profile as a health care advocate.

Since her Rose Garden debut, Mangat says she’s been invited to attend other Florida political events, including some hosted by Sen. Bill Nelson, D-Fla. She sometimes gets invited to stand on stage, or to sit in a V.I.P. area. But she’s not eager to be just another human prop. “It’s kind of a let-down after you’ve been in the [Oval] Office, talking to the president,” Mangat said.