How was the America 250 exhibit at DC's Smithsonian Castle curated?

How was the America 250 exhibit at DC's Smithsonian Castle curated? Tasked with finding 15 objects that tell the story of the first 250 years of the United States, Abeer Saha and a team of curators had a selection of more than 150 million items to pick from through the Smithsonian's vast…