New York (AFP) - Once the golden hope of the 2016 Republican ticket for the White House but now the butt of frontrunner Donald Trump's mockery, Jeb Bush has called on his mother to help him win.

The 90-year-old former first lady, whose husband and eldest son have already served as US president, famously advised her second son Jeb against running for the White House.

But it seems she has changed her mind.

"Jeb has been a very good father, a wonderful son, a hard worker -- his heart is big," she says, elegantly coiffed and turned out in blouse and pearls for the 34-second video released by his campaign on Friday.

"When push comes to shove people are going to realize Jeb has real solutions, rather than talking about how popular they are, or how great they are.

"He's doing it because he sees a huge need and it's not being filled by anybody. Of all the people running, he seems to be the one who could solve the problems. I think he'll be a great president," she adds.

The 62-year-old former Florida governor raised vast sums of money but struggled to retain voter interest in a campaign dominated by the brash, insult-dishing billionaire and TV celebrity Trump.

To ram the message home, Bush's campaign also released a copy of a hand-written letter by the former first lady in which he explains her change of heart.

"People ask me if I wanted Jeb to run. The answer was no as the sacrifice for his family was huge. I changed my mind as it became clear that he is needed. I admit to being prejudiced as I am his mother," says the letter.

Barbara made headlines in April 2013 by announcing in an interview that she did not want to see Jeb follow his father and older brother into the White House.

"There are other people out there that are very qualified and we've had enough Bushes," she said on NBC television.

The latest Quinnipiac University poll for Iowa, which casts the first votes in the election process on February 1, put Bush in a tie for sixth place with three percent of likely Republican caucus-goers. Trump led the way with 31 percent.