Thomas B. Edsall, The Huffington Post

Hillary Clinton has summoned top donors and backers to attend her New York speech tomorrow night in an unusual move that is being widely interpreted to mean she plans to soon suspend her campaign and endorse Barack Obama — not tomorrow night but within a day or two.

Obama and Clinton spoke Sunday night and agreed that their staffs should begin negotiations over post-primary activities, according to reliable sources. In addition to seeking Obama’s help in raising money to pay off some $20 million-plus in debts, Clinton is known to want Obama to assist black officials who endorsed her and who are now taking constituent heat, including, in some cases, primary challenges from pro-Obama politicians.

“This has never happened before,” one donor said, referring to the personalized request by email to attend the event in New York Tuesday night.

Obama is expected to claim enough delegates to put him over the top that night at a separate event in St. Paul.

In an afternoon conference call today with about two dozen top fundraisers, Clinton strategist Harold Ickes spoke in very conciliatory terms about Obama, in contrast to his tougher rhetoric in public and on television, according to sources. He told the participants that Clinton wants to “significantly” help Obama, but he did not go so far as saying that she will announce withdrawal — that is the prerogative of the candidate.

Ickes told the group to “take a deep breath” and let Clinton proceed in her own fashion.

Earlier in the day it was reported that Clinton staffers were being urged by the campaign’s finance department “to turn in their outstanding expense receipts by the end of the week,” another sign that the run at the White House was nearing an end. In addition, Politico wrote that members of Clinton’s advance staff had received calls and emails Sunday night, summoning them to New York City and telling them their roles on the campaign are ending.