Washington  - Even world leaders need some time off from the daily grind of international crises and political infighting, and US President Barack Obama may need it more than most.

Obama heads into vacation Friday afternoon after a bruising eight months in office, tackling the worst economic downturn since the Great Depression, ongoing wars in Afghanistan and Iraq, terrorism and a struggle to close Guantanamo Bay.

With his wife, Michelle, and their young daughters, Sasha and Malia, Obama will head to the presidential retreat at Camp David in Maryland for the weekend. On Sunday, they will begin an eight-day stay at Martha's Vineyard, a jet-set resort island in Massachusetts.

Martha's Vineyard is a vacation spot enjoyed by celebrities and past presidents including Ulysses S Grant, Richard Nixon and Bill Clinton, who spent six summers there in the 1990s.

But a president can never take a real vacation.

Former president George HW Bush spent one summer break dealing with the collapse of the Soviet Union and another with Iraq's 1990 invasion of Kuwait, which led to the Gulf War that followed.

His son and Obama's predecessor, George W Bush, was often criticized for vacationing for too long, spending up to a month at his ranch in Crawford, Texas.

But the younger Bush held briefings with staff and reporters during his time at the ranch and even hosted foreign leaders. The rare invitations to the ranch became the highest mark of personal respect that Bush could convey on his counterparts, even above the pomp of a White House meeting.

Obama's vacation is a short one by presidential standards. He leaves plenty of challenges simmering back in Washington.

Domestically, Obama's hopes for health-care reform are under threat, and the sputtering economy is only just starting to come out of recession. Despite his pledge to change Washington's culture, Congress remains as deadlocked and partisan as ever.

The US will be watching closely in the aftermath of Afghanistan's presidential elections Thursday. A recent spike in violence in Iraq, since US forces pulled back from the country's cities in June, could become another distraction.

The bickering over health care is widely blamed for Obama's falling popularity in recent weeks. A poll by the Pew Research Centre this week put his approval rating at 51 per cent, down from 61 per cent in June.

Perception is everything when a president goes on holiday. Obama will be given some leeway by the public to relax, but has to be careful to avoid being seen as living it up in a time of economic dislocation.

Ever the politician, Obama has reportedly rented out a 28-acre estate owned by two donors to the opposition Republican Party. But the estimated price tag of at least 35,000 dollars, which Obama will pay out of his own pocket, has raised some eyebrows.

Some protests are likely to follow Obama up to Martha's Vineyard. Cindy Sheehan, who made a name for herself protesting the Iraq War outside Bush's ranch in 2004, has indicated she will head up to the island. (dpa)