The spat reflects an emerging rift between Trump disciples and the party.
But Don Jr, who is thought to have political aspirations of his own, reserved his ire for those who may be eyeing up a presidential run in 2024.
“They have a perfect platform to show that they’re willing & able to fight but they will cower to the media mob instead. Don’t worry @realDonaldTrump will fight & they can watch as usual!”
She is widely thought to be preparing a White House bid in 2024.
Mr Trump Jr continued: “Republicans have been weak for decades which has allowed for the left to do these things.”
His brother, Eric, tweeted: “Where are Republicans! Have some backbone. Fight against this fraud. Our voters will never forget you if your [sic] sheep!”
The two men went on to name and praise Republicans they deemed to have been vocal in defence of their father.
Other Trump backers also piled on and took aim at Ms Haley in particular. Matt Gaetz, a Florida congressman, tweeted: “While some of us are fighting for President Trump… Nikki Haley is eulogising him. Sad!”
In his four years in politics, Mr Trump has managed to bend the Republican party to his will, consistently achieving above 90% approval ratings from self-identified party members.
The party manifesto this year was scrapped and replaced by a pledge to “support the president’s America-first agenda”.
This row between the Trumps and the party establishment will raise questions about which direction the party goes after Trump departs, whether that is in 2020 or 2024. (BBC)