(CNN) - President Barack Obama and first lady Michelle Obama mark the 11th anniversary of the 9/11 attacks with a moment of silence on the South Lawn of the White House. They then attend the September 11th Observance Ceremony at the Pentagon, and the president later visits Walter Reed National Military Medical Center.
Meanwhile Vice President Joe Biden attends the Flight 93 National Memorial Commemorative Service in Somerset County, Pennsylvania.
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GOP presidential nominee Mitt Romney addresses a National Guard Association Convention in Reno, Nevada, while his running mate, Rep. Paul Ryan, spends the day at his home in Janesville, Wisconsin on Tuesday.
Elsewhere on the trail, former President Bill Clinton attends a campaign event for Obama in Miami.
Schedule of campaign events:
2 p.m. ET - Romney Addresses National Guard Association Convention in Reno, Nevada.
5:30 p.m. ET - Clinton delivers remarks at a campaign event at Florida International University.