Kurin wouldn’t pronounce the Bubble project dead, saying officials needed to step back and figure out how best to move forward, but Koshalek’s resignation makes the already endangered project far less likely.

The 145-foot-tall Bubble, which would inflate for two months every fall, providing a transformative architectural and cultural space on the Mall, has been the signature project of Koshalek, who served as director of the Museum of Contemporary Art in Los Angeles for nearly 20 years. The Bubble’s announcement was called visionary, ambitious and potentially uplifting. The design, by New York architectural firm Diller Scofidio + Renfro, won a progressive architecture award from Architect, the magazine of the American Institute of Architects, in 2011.

Problems arose when construction cost estimates rose from about $5 million to $15.5 million. A series of board resignations has hampered the museum’s ability to raise funds, and the project has been delayed at least three times. Since 2010, when Bloomberg LP donated more than $1 million, there have been no gift announcements.

The board meeting comes a little more than a week after an internal report by a four-person team convened by Kurin, the Smithsonian’s undersecretary for history, art and culture, concluded that the Bubble’s annual programming costs would exceed revenue by about $2.8 million.

The report, obtained by The Washington Post, said the Bubble would have operated at about a $1.4 million deficit as a “Center for Creative Dialogue,” hosting high-level arts and cultural conversations akin to those featured in TED talks or sponsored by the Aspen Institute. The deficit would be slightly more than $450,000 as a “Special Events Venue,” hosting daytime and evening events. And as a free “Public Program Venue,” with dialogues, performances and art installations, the Bubble would lose about $960,000. In addition to the shortfall, each of the three scenarios raised questions of the project’s impact on current Hirshhorn programming, fundraising and staff, competition with other venues, and its connection to the Hirshhorn or Smithsonian mission.

Last fall, Koshalek called the Bubble essential to the future of the Hirshhorn. “It has to be controversial and highly experimental, otherwise it wouldn’t represent the reality of contemporary art and culture,” he told The Washington Post. That reality comes with inherent tensions, he said. “There’s no way you can avoid it. No way you should avoid it.”

Koshalek pioneered a number of programs at the Art Center College of Design in Pasadena, Calif., but was ousted after a planned expansion by architect Frank Gehry sparked a backlash from students, faculty and alumni on the campus and was ultimately not built.

Kurin says the board’s indecision “wasn’t about the inherent quality of the architecture, which is almost universally regarded, and it wasn’t about the content of the programs,” Kurin says. “It was about sustaining the cost and paying for all this in a time of tough fundraising.”

“I was chair of the search committee that hired Richard, Kurin said. I have nothing but admiration for his creativity and vigor. He’s done great things over at the Hirshhorn.”