Constance Caplan, chair of the Hirshhorn Museum board of trustees, announced her resignation on Monday following an exodus that has included the museum's director and other board members.

Former director Richard Koshalek's proposed and unrealized $12.5 million Seasonal Inflatable Structure project, informally known as the “Bubble,” was one issue that brought the Washington, DC, museum to a boiling point.

Caplan's strongly-worded resignation letter was acquired by the Washington Post on Wednesday.

She writes, "...my decision is based on a series of events these past few months that I have found increasingly troubling, and that have led me to prefer not to remain involved with the Museum and the Smithsonian at this time."

"What disturbs me is the contentious manner and lack of inclusiveness with which a number of trustees and staff associated with the Hirshhorn and the Smithsonian have behaved over the past year — factors that also led to the resignations of the prior Board Chair, the Director, and several key Trustees," says Caplan.