Trump mocks Jeb’s campaign appearance with brother

Republican presidential front-runner Donald TrumpDonald John TrumpKoch-backed group launches six-figure ad buy against Heitkamp Anti-abortion Dem wins primary fight Lipinski holds slim lead in tough Illinois primary fight MORE early Monday mocked rival Jeb Bush for a scheduled campaign appearance with the former Florida governor’s brother, former President George W. Bush.

Trump tweeted that it was “funny” that Jeb Bush didn’t “want help from his family in his failed campaign and didn’t even want to use his last name.”

Trump asked in a later Tweet if George W. Bush's appearance means he is "fair game" for questions about the World Trade Center, Iraq War and "eco collapse."

Jeb Bush and George W. Bush are scheduled to appear together at their first campaign rally Monday evening in North Charleston, S.C., ahead of the Palmetto State’s primary.

George W. Bush, who is popular in South Carolina, last week was featured in a radio ad in which he touted his brother as a "steady leader."

"We live in troubled times, with the military deployed around the world. We need a strong leader with experience, ideas and resolve," the former president says in the ad.

Jeb Bush, coming off a fourth-place finish in the New Hampshire primary, is averaging 10 percent support in South Carolina, behind Trump, Ted CruzRafael (Ted) Edward CruzCruz says Cambridge Analytica assured him its practices were legal Dem battling Cruz in Texas: ‘I can understand how people think this is crazy’ Overnight Tech: Facebook faces crisis over Cambridge Analytica data | Lawmakers demand answers | What to watch for next | Day one of AT&T's merger trial | Self-driving Uber car kills pedestrian MORE, Marco RubioMarco Antonio RubioRubio: McCabe 'should've been allowed to finish through the weekend' For Tillerson, bucking Trump became a job-killer At least six dead after pedestrian bridge collapses on cars in Florida MORE and John Kasich.

Trump earlier this month said Jeb Bush "had to bring in mommy” for help after Barbara Bush said it was “unbelievable” to think that women could support the real estate mogul.

“Wow, Jeb Bush, whose campaign is a total disaster, had to bring in mommy to take a slap at me,” Trump tweeted then. “Not nice!”

--This report was updated at 9:07 a.m.