You mean his brother from another mother ?
In his response, Cruz showed more class than GWB:
I have great respect for George W Bush, and was proud to work on his 2000 campaign and in his administration,” Cruz said. “It’s no surprise that President Bush is supporting his brother and attacking the candidates he believes pose a threat to his campaign. I have no intention of reciprocating. I met my wife Heidi working on his campaign, and so I will always be grateful to him.”