George W Bush enters campaign for Jeb Bush in South Carolina with veiled attacks on Donald Trump

Commentators suggest it is rich for the man who started two wars over 9/11 to criticise Trump for 'mirroring the nation's anger and frustrations'

Republican presidential candidate and former Florida Gov. Jeb Bush, left, shakes hands with his brother former President George W. Bush (AP)

George W Bush has appeared at his first campaign rally for his brother Jeb – but while he purported to set out a positive case for extending his family’s legacy in the White House, he reserved his strongest words for barbed attacks against Republican frontrunner Donald Trump.

At no point did the former president actually mention the billionaire businessman by name – but it was clear he was referring to the powerful anti-establishment movement that has elevated Mr Trump to pole position when he said: “I understand Americans are angry and frustrated.”

His next words, coming from the man who started the Iraq War as a retaliation for the 9/11 attacks, were criticised as hypocritical by some observers. Warning against a Trump vote, he said: “But we do not need somebody in the Oval Office who mirrors and inflames our anger and frustration.”

The shadow of George W has hung over Jeb Bush since the start of the presidential campaign, with attacks on his brother’s legacy proving popular among other candidates.

On Monday, ahead of the former president’s campaign rally appearance, Mr Trump tweeted: “Now that George Bush is campaigning for Jeb(!). is he fair game for questions about World Trade Center, Iraq War and eco collapse? Careful!”

Opinions on George W Bush’s legacy are divided within the Republican party. In a TV debate on Saturday night, Mr Trump repeatedly claimed the simple fact that the 9/11 attacks happened on the Bush watch meant the family could not keep the country “safe”.

Donald Trump, left, and fellow candidate Jeb Bush speaking at the debate (EPA)

But speaking to Politico afterwards, unnamed party insiders said the attacks on the last Republican president were “galactic-level stupid”, “mean-spirited” and “unpresidential”.

While Mr Trump has a track record of causing outrage and seeing his lead in the race for the Republican nomination only rise, it is early favourite Jeb Bush’s hopes that are now in peril.

Bush is vying with Florida senator Marco Rubio and Ohio governor John Kasich for the role of mainstream contender to the conservative ticket of either Mr Trump or Texas senator Ted Cruz.

And in implicit criticism of the latter two on Monday night, George W urged voters to back a candidate who will be “measured and thoughtful” and exhibit “humility” on the world stage.

“All the sloganeering and all the talk doesn't matter if we don't win,” George W said. “We need somebody who can take a positive message across the country.”

George W. Bush has kept a low profile since leaving the White House in early 2009. He retreated to his home state of Texas, where he picked up painting and delved into work on his presidential library, public health projects in Africa, and events for wounded military service members.

He joins the trail in South Carolina after the influence of family matriarch Barbara Bush failed to secure much of a lift in votes for Jeb in New Hampshire.

Additional reporting by agencies