WASHINGTON — President Trump’s grip on his party slipped on Thursday as anger boiled over among Senate Republicans about a growing list of issues. In a striking display of defiance, GOP senators abruptly derailed plans to vote on legislation to fund Trump’s immigration crackdown amid deep disagreements over security funding for a White House ballroom and a $1.8-billion fund to pay people who claim to have been politically persecuted. The discontent had been building for weeks. Many senators had grown frustrated over Trump’s decision to endorse candidates running against longtime Republican incumbents. Others, worried about rising costs as a result from the war in Iran, had aired concerns ahead of the midterm elections. But the breaking point came when the Justice Department, with little warning, pushed to create what it termed the “anti-weaponization fund.” Senate Majority Leader John Thune (R-S.D.) acknowledged the concerns over the fund Thursday after a reportedly contentious private meeting about it between Senate Republicans and acting Atty. Gen. Todd Blanche. He also conceded midterm politics had added to the tension. “It’s hard to …