WASHINGTON  Nancy Larson’s most difficult conversation was, by far, the one with Chelsea Clinton.

“It was just heartbreaking,” said Mrs. Larson, a Democratic National Committee member from Minnesota and, more to the point, a superdelegate who had initially pledged herself to Senator Hillary Rodham Clinton. This was last Saturday, after the former first daughter learned that Mrs. Larson would be shifting her allegiance to Senator Barack Obama.

“She is a delightful young woman who loves her mother very much,” Mrs. Larson said. “She was really pushing me. She kept asking me why I was doing this. She just kept asking, ‘Why? Why?’ ”

It is a question many in the Clinton camp are asking these days, sometimes in conversations far less civil than that one. After nearly two decades building relationships with a generation of Democrats, Mrs. Clinton has recently suffered a steady erosion of support for her presidential campaign from the party stalwarts who once formed the basis of her perceived juggernaut of “inevitability.”

Some of it is just business, practical politicians putting aside ties to the Clintons to follow the will of the voters in their states or making a calculation about who seems best positioned to win.