Rahm Emanuel's expected departure as President Barack Obama's chief of staff may be just the start of wholesale personnel changes at the White House after what's predicted to be a devastating midterm election for Democrats.

In the fast-paced, high-pressure White House atmosphere, two years can take its toll on people, and Obama aides say changes are coming.

"This is a time in which people who have given two years of service return to things that they were doing beforehand," White House press secretary Robert Gibbs said. "I don't doubt that that will happen in ... this administration like it has in many of the previous."

Indeed, staff shake-ups are a White House tradition, particularly after elections or when things go badly for a president. But the changes usually don't affect the direction of policy or the course of a presidency. Americans generally judge a president by his decisions and the country's well being, not by staff aides who are largely unknown to the public.

Gibbs, who has been with Obama since his Senate days, is among those whose role could change. He's thought to want a more advisory role, with deputy spokesman Bill Burton the likely candidate to take over the briefing room podium.

Emanuel is expected to return to Chicago to run for mayor now that longtime Mayor Richard Daley has announced he won't seek re-election.

Senior adviser David Axelrod, one of the masterminds behind Obama's presidential bid, could be summoned to run the 2012 re-election campaign. Others also will be called upon to join that effort, either here in Washington or in Chicago, though aides say they haven't been asked to commit to the campaign yet.

Changes are also afoot among the president's national security team. Defense Secretary Robert Gates, a holdover from George W. Bush's administration, already has said he plans to step down next year. It's widely believed that national security adviser James Jones will leave the administration as well.

Looming over the speculation of staff changes is the public's dissatisfaction with the direction the country is taking and the myriad polls suggesting Democrats could face major losses in November. Similar scenarios have led to shake-ups under previous presidents as the administration looked to right its course.

Former President Bill Clinton lost his first chief of staff, Mack McLarty, ahead of the 1994 midterm elections in a shake-up aimed at improving White House operations. More staffers, including press secretary Dee Dee Myers, left after Democrats went on to suffer disastrous defeats.

Though Bush kept much of his high-level staff in place through his first term, the Republican Party's losses in the 2006 midterms sent top advisers packing, including Defense Secretary Donald H. Rumsfeld, chief political strategist Karl Rove, counselor Dan Bartlett and chief attorney Harriet Miers.

"Two years is about as long as anyone should try to stay at the White House," said Tony Fratto, a former Bush official who joined the White House amid the second-term staff changes. "Having new people with fresh legs is smart."

Obama's staff has stayed relatively intact through his first 18 months in office, though there have been two high-profile departures on the economic team: budget director Peter Orszag and the head of the Council of Economic Advisers, Christina Romer, who both resigned this summer. The communications team also saw shake-ups early on when communications director Ellen Moran left within the administration's first 100 days. The post was temporarily filled by Anita Dunn before Obama named Dan Pfeiffer as her permanent replacement.

For Emanuel, Daley's surprising decision not to run presents an opportunity to make a graceful exit after a tenure that could be viewed as a legislative success, but perhaps not a political one.

In a White House that prides itself on message control, senior officials appear to be laying the groundwork for his departure.

"Obviously something like that doesn't come around a lot," Gibbs said. "I presume that Rahm will take some time and make a decision about that."

The president himself went a step further, declaring in an interview Thursday that Emanuel would be "a terrific mayor," though he thought Emanuel would wait until after the Nov. 2 midterm elections before making a decision.

While election rules in Chicago give candidates until Nov. 22 to file petitions to run, it's likely Emanuel would have to start building a campaign operation earlier than that in order to make a viable bid in a competitive race. Some Obama aides could leave the White House to join Emanuel's campaign.

Among those rumored to be pursuing the chief of staff job should Emanuel leave are deputy national security adviser Tom Donilon, legislative affairs director Phil Schiliro and Ron Klain, Vice President Joe Biden's chief of staff.

Senior adviser and longtime Obama friend Valerie Jarrett also has been mentioned, though given her close relationship with Obama, it's likely she could have already had the chief of staff job if she wanted it.