(Alan Diaz/AP Photo)

First Lady Michelle Obama and Dr. Jill Biden were grand marshals at today’s NASCAR season finale at Homestead-Miami Speedway, appearing as part of their charitable campaign to support military veterans and their families.

But their benign, bipartisan cause wasn’t enough to prevent public fallout from the nation’s polarized political climate as they were introduced before the crowd.

ESPN video from the event documented loud boos from some in the stands as the announcer named Obama and Biden, seconds before they delivered the “most famous words in motorsports,” telling drivers to start their engines.

The pair — who co-chair the Joining Forces initiative — stood beside retired Army Sgt. Andrew Barry and his family. Barry was wounded in action in Iraq and Afghanistan, retired from the military in 2009 and now volunteers at an Orlando veterans center, the announcer said. He received resounding applause.

A source traveling with the first lady downplayed the incident, telling ABC News there was no discernible booing during the “loud chaotic program with jets flying over and tons of noise.”

The Associated Press reported that the two women received a standing ovation at the pre-race meeting with drivers, during which Obama said NASCAR was “amazing in terms of its support, not just today but every day, for military families.”

Before the race, the first lady addressed a barbeque for military families that NASCAR had invited to the event.

“Everyone around the country is focused on you.  And this isn’t just an effort today,” she said. “ Jill and I through Joining Forces, we want to make this a part of the dialogue in this country forever.  Whether Jill or I are here or not, whether this administration is here or not, this is about the way we want this country to talk about our troops, veterans and military families forever.  We want you to feel that appreciation and that gratitude so that you know your sacrifice is not in vain.”

The negative reaction from fans was first reported by Mediaite.