President Barack Obama has had to preside over a half-dozen memorial services following shootings, tornadoes, mine accidents and other tragedies since he took office in 2009, including this service following the 2011 shooting in Tucson, Arizona. Here is a look at those moments:
November 10, 2009 -- Maj. Nidal Hasan is charged with killing 13 people at Fort Hood in November, 2009, called the worst incident of its kind on a military base. Speaking to an estimated 15,000 people at a memorial...
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