Donald Trump was formally nominated as his party’s presidential candidate as Republicans kicked off their national convention Monday under heightened security concerns and an ongoing investigation into the attempt on his life during a weekend campaign rally in Western Pennsylvania.The former president pledged resilience in his first media interviews following the attempted assassination Saturday at a fairgrounds in Butler, Pa. He said his brush with death had prompted him to “throw out” the speech that he’d planned to deliver to party delegates at the Milwaukee convention later this week.Instead, he told the New York Post, he was drafting a new address that he hoped would “unite our country” but added: “I don’t know if that’s possible.”Meanwhile, federal authorities reported only halting progress Monday in their efforts to determine what motivated Thomas Matthew Crooks, the 20-year-old Allegheny County man they’ve identified as Trump’s would-be assassin, as finger-pointing and recriminations continued surrounding the failure of security protocols that allowed him to get so close to the rally stage.Leaders of three congressional committees announced plans to hold hearings, with the House Committee on Oversight announcing it would kick things off with testimony next week from Kimberly Cheatle, the director of the U.S. Secret Service.Cheatle defended her agency’s handling of the Butler rally in a statement — her first since the thwarted attempt on Trump’s life. She also expressed confidence in the Secret Service’s RNC security plans.“The Secret Service is working with all involved federal, state, and local agencies to understand what happened, how it happened and how we can prevent an incident like this from ever taking place again,” Cheatle said.The day also delivered Trump a series of significant wins. In addition to receiving the official GOP nomination during a rollcall vote from the convention floor, he revealed his pick for vice president — U.S. Sen. JD Vance of Ohio — and scored a significant legal victory in one of the three remaining criminal cases pending against him.A federal judge in Florida dismissed charges that Trump had mishandled classified documents after leaving the White House, ruling that Special Counsel Jack Smith, whose office had brought the case, had been improperly appointed and was, therefore, illegally prosecutingThe decision, which broke with years of precedent, drew scrutiny from legal experts. Smith’s office, through a spokesperson, vowed to appeal.But while Trump had pledged unity in the interviews he gave conservative media just hours before, he greeted ...