President Obama's return to Washington on Sunday remains shrouded in mystery, with aides providing few details of why the president is leaving his Martha's Vineyard vacation home to come to the White House.
Here's what we we know so far.
The jaunt has been scheduled for weeks, so it is not in reaction to late developing events like the unrest in Ferguson, Mo., or the airstrikes the president ordered last week in Iraq.
Press secretary Josh Earnest said he “wouldn't be surprised” if the president had conversations about Iraq while he was back at the White House, but that “there are other meetings in the schedule, too.”
Deepening the mystery is the insistence by White House spokesman Eric Schultz that staffers did not “anticipate any major significant news developments out of Washington those few days.”
Schultz said specifically that the president would not make any major announcements on immigration reform, and the deputy press secretary — who is serving as the top administration spokesman while Earnest is on paternity leave — will remain on Martha's Vineyard while the president returns to Washington.
The decision to interrupt the president's vacation is highly unusual.
In 2012, the president returned from Hawaii to Washington to oversee fiscal-cliff negotiations, only to return after signing a bipartisan compromise.
But such maneuvers are rare and costly — documents obtained by the conservative watchdog group Judicial Watch suggest the president's roundtrip travel to Martha's Vineyard costs more than $1.1 million — and there is no pressing legislative business in Washington.
Here's five reasons the president could be traveling back to Washington.
Foreign leader visit
There's some chance that the president could plan to huddle with a fellow head of state at the White House. Such visits are usually announced months in advance, but occasionally the administration opts against providing reporters with a heads-up — especially if leaders are visiting from volatile areas like the Middle East.
That Biden, who has been a key actor for the administration on recent crises in Iraq and Ukraine, is scheduled to meet with the president gives this theory some credence.
Still, there’s no reason a foreign leader couldn't visit the president at Martha's Vineyard. During George W. Bush's presidency, heads of state — including, memorably, Russian President Vladimir Putin — traveled to his ranch in Crawford, Texas, to meet while the president was vacationing. Bush’s father, former President George H.W. Bush, hosted Israeli Prime Minister Yitzhak Rabin and British Prime Minister John Major at the family compound in Kennebunkport.
There’s also been no indication in foreign media that a world leader is planning an extended trip to Washington.
All-staff strategy meeting
It's no secret that the president is limping into the midterm elections.
A poll released Monday by McClatchy found that voters are less likely to vote for congressional Democrats because they are disappointed with the president. By a 42-32 percent margin, voters say that because of the president, they’re more likely to vote for a Republican candidate this fall. And, for the first time, Republicans are winning the generic ballot measure, with voters more likely to say they’d vote for a GOP candidate by a 43-38 percent margin.
Obama may be bringing in his top advisers past and present to figure out how to help Democrats battling to retain the Senate, and remain relevant as he enters the lame-duck portion of his presidency.
Or the president could use his time in Washington simply to rally his beleaguered staff. In summers past, presidents have hosted barbecues or other large social events for aides and their families.
Obama library pow-wow
The president and White House officials have largely steered clear of discussions of a future presidential library site and the inevitable lame-duck implications that come with such talks.
The foundation charged with developing the president's future library is in the midst of sorting through 13 initial bids from universities and cities interested in hosting the center.
Obama could use the time in his office to pore over the bids and begin making decisions on where his post-presidential operating base will be.
While speculation has focused on Chicago as the probable site for the library, senior presidential adviser Valerie Jarrett said in June that no city had a lock on the site.
Surprise trip abroad
It's quite possible that the White House could be faking out reporters by claiming the president plans to travel back to Washington.
The administration strives to keep presidential travel to countries like Afghanistan and Iraq under wraps until the president arrives, out of concern for the president's security.
Over Memorial Day, only a small handful of reporters who traveled with the president aboard Air Force One were told of Obama's plans to travel to Afghanistan before he arrived.
Afghanistan's rival presidential candidates agreed earlier this month to a deal to resolve their election dispute after negotiations with Secretary of State John Kerry. Obama could visit Kabul to celebrate that diplomatic breakthrough and build momentum for a status of forces agreement that will allow for the gradual withdrawal of U.S. forces.
With conflicts raging in Gaza, Iraq and Syria, there are other hotspots where a presidential visit could prove influential — and dangerous enough the White House would want to keep it a secret.
Driver's license for Malia?
With White House officials insisting that the president doesn't intend to make big news, there’s some speculation the return could be related to his family.
The elder Obama daughter, Malia, turned 16 earlier this summer, and is returning to Washington with the president.
The White House is fiercely protective of the daughters and rarely provides information about their lives or whereabouts. But we know Malia has spent her summer interning on the set of a television show in California, visiting colleges and even taking in Chicago's annual Lollapalooza concert festival.
Could the president have a father-daughter trip to the DMV planned? In 1996, then-President Clinton memorably took his daughter, Chelsea, to Camp David for a driving lesson.
One thing we do know — the president doesn't plan to be behind the wheel, helping Malia learn to drive by himself.
“I think our agents don’t want us driving with teenagers,” first lady Michelle ObamaMichelle ObamaFLOTUS tweets her thanks GOP senator: Obama is ‘a good role model’ Democrat explains why she's going to Trump's inauguration MORE told “Live with Kelly and Michael” earlier this year. “I don’t think they want [the president] in the state when she’s learning how to drive. We will, fortunately, be able to hand that responsibility over to someone else.”