President Trump’s eldest son has abruptly canceled his scheduled appearance at a fundraiser next week for Texas Republican George P. Bush amid escalating tensions between the two political families, a source familiar with the discussions confirmed Tuesday.

Donald Trump Jr. was planning to headline a June 25 fundraiser in New York for Bush, the Texas land commissioner running for re-election this fall. But he pulled out after members of the Bush family publicly condemned the Trump administration’s policy of separating migrant children from their parents and detaining them at the border.

George P. Bush’s father, former Florida governor Jeb Bush, and his aunt, former first lady Laura Bush, sharply criticized the family-separation policy as cruel and inhumane.

Trump Jr.’s cancellation was first reported by Axios.

Trump Jr. had forged a political friendship with George P. Bush despite the open hostility between their fathers after the bruising 2016 Republican presidential primaries. In the general election, George P. Bush endorsed Trump, even as some in his family resisted the then-nominee, and this year the president endorsed Bush’s re-election as land commissioner.

But after Jeb Bush took what Trump family members interpreted as a swipe at Trump – saying in a March appearance at Yale University that he goes home to children “who still love me” – Trump Jr. warned George P. Bush that if Jeb Bush did not stop attacking his father there would be consequences, according to a person close to Trump Jr., who spoke on the condition of anonymity to relate private conversations.

This person described George P. Bush as apologetic and said he told Trump Jr. that he already had talked to Jeb Bush about the situation. For Trump Jr., Jeb Bush’s tweet Monday about family separation was the last straw, according to this person.

“Don likes George P. personally but felt like Jeb’s continued attacks put him in a position where he could not do the fundraiser, and so after the latest one he decided to pull the plug,” said the person close to Trump Jr.

Jeb Bush tweeted Monday, in response to one of the president’s tweets: “Children shouldn’t be used as a negotiating tool. @realDonaldTrump should end this heartless policy and Congress should get an immigration deal done that provides for asylum reform, border security and a path to citizenship for Dreamers.”

“Dreamers” refers to immigrants brought to the United States illegally as children.

The comments came after Laura Bush wrote a scathing editorial about the policy in The Washington Post. She wrote: “I live in a border state. I appreciate the need to enforce and protect our international boundaries, but this zero-tolerance policy is cruel. It is immoral. And it breaks my heart.”

The former first lady went on to say that the images from the border “are eerily reminiscent of the internment camps for U.S. citizens and noncitizens of Japanese descent during World War II, now considered to have been one of the most shameful episodes in U.S. history.”