First Lady Michelle Obama is putting her most valuable asset as first lady on the line: her sky-high popularity.

By entering the national debate over guns - calling for a vote on gun-control bills today, and tearing up as she talked about the death of a Chicago teen - the first lady is wading directly into a highly charged political issue for the first time in her husband's presidency.

"Right now my husband is fighting as hard as he can and engaging as many people as he can to pass common-sense reforms to protect our children from gun violence," she told a luncheon gathering in Chicago today, kicking off a new venture to curb youth violence. "And these reforms deserve a vote in Congress."

That call to political action may signal a new, more controversial phase of her tenure as first lady. It could also mark an inflection point in the way she's viewed by the public, depending on how this plays out.

Michelle Obama is consistently ranked among the most popular political figures in the country. An ABC News/Washington Post poll taken shortly before the November election found her viewed favorably by 69 percent of respondents, and unfavorably by just 26 percent - and that in the heat of a bitter presidential campaign.

She got to that level by being mostly apolitical. Few first ladies have been more visible, but her highest-profile projects have been in support of military families and against childhood obesity, hardly areas of great controversy.

Nothing in Michelle Obama's history or recent actions suggest she's about to embrace policy to the level that Hillary Rodham Clinton did as first lady. But today's speech was a strong hint that Mrs. Obama is viewing her role in a second term differently from the way she did in the first.

It may be that recent shootings have made an impact on her as a mother, much as the president has talked about being hit as a father by the tragedy in Sandy Hook. The first lady choked back tears talking about a 15-year-old killed in a shooting just a week after coming to Washington for President Obama's second inauguration.

"Hadiya Pendleton was me and I was her. But I got to grow up and go to Princeton and Harvard Law School and have a career and a family and the most blessed life I could ever imagine," she said.

"And Hadiya, well, we know that story," Mrs. Obama continued. "She went to a park with some friends and got shot in the back."