First lady Michelle Obama entered the health care fray Tuesday, signing an e-mail sent to millions of Democratic donors and activists that asks support for her husband’s plan to overhaul the nation’s health care system. “I’ve just launched United We Serve, a national initiative to tackle our toughest problems by working hand-in-hand in communities across the country,— the popular first lady wrote. “We aim to make a real difference right now and bring more and more Americans into a tradition of life-long service to make an even greater difference down the road.—“I’d like to invite you to be a part of it by joining Organizing for America’s National Health Care Day of Service this weekend,— she continued. “You can join up with other local OFA supporters to help improve health care services in your community and make a difference as we work to reform America’s health care system.—Obama’s message was blasted to the combined e-mail lists of the Democratic National Committee and Organizing for America, the grass-roots lobbying group that inherited President Barack Obama’s 13 million-plus cache of e-mail addresses and cell phone numbers from his presidential campaign. As he has made his case for health care reform, President Obama’s approval ratings have dipped to less than 60 percent in recent weeks, according to surveys available on Pollster.com. Meanwhile, Michelle Obama appears to continue to enjoy wide public support. In a poll earlier this spring, 72 percent of those surveyed by Gallup Poll had a positive impression of the first lady, compared with 69 percent for her husband.