Former President George W Bush has hit the campaign trail to boost younger brother Jeb's faltering presidential nomination bid.
He met veterans and appeared at a rally in South Carolina on Monday, ahead of Saturday's primary election.
George W Bush's legacy has come under fierce attack from Republican frontrunner Donald Trump.
Jeb Bush, the former Florida governor, has spent a lot of campaign cash but failed to make an impact.
He is struggling to catch up with Mr Trump and Texas Senator Ted Cruz, who won the New Hampshire and Iowa contests respectively.
Mr Bush's famous family has largely kept out of his presidential nomination battle and he insisted last year that he was running as his own man.
But last week his mother Barbara Bush, wife of former President George HW Bush, spoke out in his support.
And on Saturday, Jeb Bush defended his brother's presidency, saying he had built a "security apparatus to keep us safe".
In a televised debate, billionaire businessman Mr Trump tore into George W Bush's record, accusing him of lying about the reasons for the Iraq War, which he said had destabilised the Middle East.
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"I want to tell you - they lied," said Mr Trump. "They said there were weapons of mass destruction, there were none. And they knew there were none."
He also scoffed at Mr Bush's defence of his brother.
"The World Trade Center came down during your brother's reign, remember that."
Experts say that Mr Trump's tactic of attacking the former president is risky because he still maintains wide appeal among Republicans in South Carolina, from churchgoers to business leaders and retired military personnel.
On Monday, George W Bush, alongside his wife Laura, met US military veterans at an American Legion Post in Columbia, South Carolina.
Last week, he praised his brother's abilities in a radio advert, and Jeb Bush will hope his personal appearance will bring dividends on polling day.
Although George W Bush remains a divisive figure nationally, he and his father both won primary elections in South Carolina.
South Carolina Senator Lindsey Graham, who quit the presidential race and is now backing Jeb Bush, said: "The Bush name is golden in my state."
While Republican voters in South Carolina make their choice for president, the Democratic Party is holding its own contest in Nevada on Saturday. Republicans in Nevada and Democrats in South Carolina get to express their views in separate contests the following week.
Mr Cruz, Mr Trump and Democrats Hillary Clinton and Bernie Sanders have all won one state each.
Key dates to come
20 February - South Carolina primary (Republican); Nevada caucus (Democrat)
23 February - Nevada caucus (R)
27 February - South Carolina primary (D)
1 March - 'Super Tuesday' - 15 states or territories decide
18-21 July - Republican convention, nominee picked
25-28 July - Democratic convention, nominee picked
8 November - US presidential elections