In a carefully-worded announcement, the Clinton campaign says the New York senator will "thank her supporters and express her support for Senator Obama and party unity."
The statement does not say that Clinton will officially concede the race to the Illinois senator, a fact that leads many observers to conclude that she will likely suspend her campaign but retain the delegates she earned during the recently-concluded primary season.
Theoretically, she could reenter the race if misfortune were to strike Obama, or if something were to emerge that shook the faith of superdelegates, the party elders and elected officials that helped Obama clinch the nomination earlier this week.
In an e-mail message to supporters, Clinton noted that she has always promised to support the Democratic nominee. She said she intends "to deliver on that promise" and that she wants to "rally the party behind Senator Obama."
Since becoming the presumptive presidential nominee earlier this week, Obama has begun to focus his attention on Senator John McCain, the presumptive Republican nominee. Both candidates have begun the process of choosing a vice presidential nominee.
Polls show most voters who backed Hillary Clinton want Obama to choose her as his running mate. Several high-profile supporters of the New York Senator have expressed the same hope. Florida Congresswoman Debbie Wasserman spoke on CBS' The Early Show.
"The best-case scenario is that Barack Obama and Hillary Clinton run together as president and vice president," Wasserman said.
Some Clinton backers have gone so far as to mount a petition drive demanding Obama offer Clinton the vice presidential slot. But one prominent Clinton ally, Pennsylvania Governor Ed Rendell, thinks any effort to force Obama's hand will be counterproductive.
"You do not bargain with the presidential nominee, even if you are Hillary Clinton and you have 18 million votes. You do not bargain," Rendell said.
Interviewed by U.S. television networks Wednesday, the Illinois senator repeatedly deflected questions about his running mate selection.
"It is premature to answer [that question]. We are going to go through a process," Obama said on CBS television. "We have a committee that is going to go through all the names [of potential vice presidential picks]. It is going to be deliberate. This is an important decision."
Clinton had no public events Thursday, while Obama is holding two campaign events in Virginia, a state that unusually votes Republican in presidential contests but which the Obama campaign thinks could fall in the Democratic column this year. John McCain is spending the day in the key battleground state of Florida.
McCain is proposing that he and Obama appear at weekly joint town hall meetings across the country between now and the November election. The Obama campaign says the idea is appealing, but that many details would have to be worked out in advance.