Obama says Michelle 'not running for president'

US President Barack Obama on Thursday scotched the notion that his more popular wife Michelle would launch a White House bid.

"There are three things that are certain in life: death, taxes and Michelle is not running for president," Obama joked as he held a discussion with voters in Louisiana.

A Harvard-trained lawyer, the first lady had struggled to find her political voice early in Obama's political career, and often seemed to abhor the crassness of day-to-day politics.

But she has since become a highly effective campaigner for her husband and has been engaged in campaigns against childhood obesity and in support of military families.

Polls have consistently shown she is more popular with the American public than her husband, raising speculative suggestions that she may run for a Senate seat or the presidency.

The Obamas leave the White House in January 2017 and have not yet announced their post-presidency plans.