Barack Obama has openly questioned why Hillary Clinton would want to go through the "undignifying process" of running for the White House in 2016.

Obama mused aloud why Clinton, who if elected would be among the oldest presidents in US history, would want to submit to another gruelling presidential campaign, eight years after she was defeated.

The US President's intervention comes as Clinton makes a bruising re-entry to the political orbit after four years as Secretary of State, a largely non-partisan job that allowed her to float above Washington mud-slinging.

In recent weeks she has toured the country to promote her new book - drawing both excited crowds of supporters urging her to run for president and heavy fire from potential Republican and Democrat adversaries.


Republicans have tried to cast Clinton, who would be 69 if she took office in 2017 - only slightly younger than Ronald Reagan - as a "20th-century candidate" out of touch with the modern world. This has dented her approval ratings, which have slipped from consistently above 60 per cent to closer to 50 per cent, a reflection of her return as a polarising figure in partisan politics.

Obama was asked by the New Yorker magazine about the prospect of both Clinton and Joe Biden, the US Vice-President, running for president in 2016.

"I think that, for both Joe and for Hillary, they've already accomplished an awful lot in their lives. The question is, do they, at this phase in their lives, want to go through the pretty undignifying process of running all over again," Obama said.

Biden, who trails far behind Clinton in polls of potential Democrat candidates, has expressed interest in running but would be 74 if he won - the oldest president ever in the White House.

The New Yorker describes Obama as unable to "hide his bewilderment that his friends would want to subject themselves to another presidential campaign".

Clinton has said she will decide by the end of the year whether to run for president, citing the forthcoming birth of her first grandchild as one reason she has not yet officially made up her mind.

But her clear interest in a second bid has revived the market for right-wing books, often thinly sourced, claiming to offer prurient details of the Clintons' private lives. Such books, last popular during Bill Clinton's presidency, have been doing a roaring trade and Blood Feud, which claims to reveal a bitter relationship between the Obamas and the Clintons, is outselling Clinton's autobiography, Hard Choices.