PHILADELPHIA (AFP) - When her husband first ran for president in 2008, Mrs Michelle Obama cautiously entered the political arena, fully supportive of his candidacy yet wary of the country's partisan battles.

Two terms later, the First Lady known for her wit, style and tact has emerged as a political force, and on Monday (July 25) she electrified the Democratic National Convention with an impassioned endorsement for Mrs Hillary Clinton that brought the crowd to its feet.

With a determined look and a big smile, Mrs Obama lauded the former first lady, making the link between the woman who would be America's first female president and her hopes for her two teenage daughters, Sasha and Malia.

"The hateful language they hear from public figures on TV does not represent the true spirit of this country," Mrs Obama said, in a thinly veiled swipe at Republican presidential nominee Donald Trump, who will battle Mrs Clinton at the polls on Nov 8.

"We know that our words and actions matter not just to our girls, but to children across this country," said the 52-year-old First Lady, a Harvard-educated lawyer.

"This election, and every election, is about who will have the power to shape our children for the next four or eight years of their lives," she said.

"There is only one person who I trust with that responsibility, only one person who I believe is truly qualified to be president of the United States, and that is our friend, Hillary Clinton," she said, before outlining the qualities of her husband's 2008 primary rival. "Hillary Clinton has never quit on anything in her life."

Armed with popularity ratings above 60 per cent, Mrs Obama knows how to captivate an audience: At the 2008 convention in Denver, Colorado, she stepped into the national spotlight with remarks that stressed her husband's commitment to American values.

That speech resurfaced last week, thanks to none other than Mr Trump. The billionaire's wife Melania introduced herself as a political spouse with words borrowed from Mrs Obama's 2008 speech.

At the 2012 convention in Charlotte, South Carolina, Mrs Obama said that even after four years as head of state, her husband was the same man.

"I have seen firsthand that being president doesn't change who you are - it reveals who you are," she said.

In stumping for Mrs Clinton, the First Lady has set aside any gripes left over from the tense 2008 campaign that saw her husband and this year's Democratic nominee exchange barbs.

"Because of Hillary Clinton, my daughters - and all our sons and daughters - now take for granted that a woman can be president of the United States," she said to the packed arena in Philadelphia.

The Obamas know that a Clinton administration is the best way to preserve the president's accomplishments, including health care reform, the Iran nuclear deal and renewed relations with Cuba, said Peter Slevin, a Northwestern University professor who wrote the First Lady's biography.

" Michelle Obama understands the political moment, recognises the importance to her husband's legacy," he said.

Her reputation as a political superstar has fueled rumors that Mrs Obama might have her own presidential ambitions.

But she has no plans to follow the lead of Mrs Clinton, also a former first lady who later become secretary of state.

"Running for political office is not Michelle Obama's thing," Prof Slevin said.

"Though she has proven to be very good at delivering political messages, at pushing policies that are important to the administration, I think she just could not bear the idea of running for office and raising money and doing all the things you have to do if you are in office."

Mrs Obama told a group of children in April that a White House bid was not in the cards.

"Hillary Clinton is an impressive woman. I will not do what she has done - I will not run for president," she said. "But there are other things that I want to do to stay involved in working in public service."

Mr Obama has also tried to cut through the speculation that the family might try to keep living at the White House.

"There are three things that are certain in life: Death, taxes and Michelle is not running for president," he said earlier this year.