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.