CHARLESTON, S.C. — George W. Bush never mentioned Donald Trump. But with his folky touch, the former president unleashed a tough takedown Monday of the billionaire businessman who has upended a Republican Party his family has long led.

“I understand Americans are angry and frustrated,” Bush said during his first campaign rally for his brother, Jeb Bush. “But we do not need somebody in the Oval Office who mirrors and inflames our anger and frustration.”

Trump's rise has confounded the Bush family and its allies. But despite months of predicting the brash billionaire would fade, it's Jeb Bush whose White House hopes are in peril, particularly if he's unable to pull out a strong showing in Saturday's South Carolina primary.

The former president emerged from his self-imposed political hibernation to try to give Bush a boost. He layered each validation of his younger brother with an implicit critique of Trump.

He urged voters to back a candidate who will be “measured and thoughtful” on the world stage.

Jeb Bush delivered an impassioned version of his campaign speech, touting his experience and vowing he could put Republicans back in the White House.

The former president's return to presidential politics has been met with blistering attacks from Trump about the unpopular Iraq war and the economic recession. Trump has also repeatedly reminded voters that the Sept. 11, 2001, terror attacks happened on Bush's watch.