The Barack Obama Presidential Center in Chicago could require a $1.5 billion endowment, its architects say, three times what was raised for the George W. Bush Presidential Center in Dallas.

Husband-and-wife architectural team Tod Williams and Billie Tsien noted that it will be difficult to raise such a huge sum because Obama scrupulously declined to do much fundraising while he was still in office.

The Obama Center is due to be so expensive because it will require the construction of both a presidential library and a museum about the lives of Barack and Michelle Obama. And federal requirements now stipulate that former presidents must have larger endowments to pay for annual operating costs at the libraries.