Former president Donald Trump reportedly further strained his relationship with Republican party leadership in Iowa after failing to show up for senator Joni Ernst's annual "Roast and Ride" charity. Except for Mr Trump, eight of the GOP 2024 presidential election hopefuls were present at the senator's charity event last month – a combination of barbecue-rally and motorcycle rides that kick off a busy summer campaign season heading into the first-in-the-nation caucuses. Florida governor Ron DeSantis, former vice president Mike Pence, US senator Tim Scott, former UN ambassador Nikki Haley and other candidates dressed for the occasion in leather and reached out to supporters. Mr Trump declared that he would not participate in the event but his campaign had expressed interest in sending videotaped remarks to be played for the crowd, according to a New York Times report. However, the former president failed to send the videotape, allegedly leaving Ms Ernst’s operation with a large bill that was wasted on renting screens for the purpose of showing the tape. The former president also potentially ruined the senator's plan to use a motorcycle helmet signed by all of the Republican candidates to sell tickets to the event. The event organisers sent the helmet to Mr Trump, who returned it later than expected and had added the numbers '45' and '47,' signaling he would be the next president. The helmet was never used, the newspaper said. The presidential hopefuls during the event all tiptoed around mentions of the 45th president. Ms Haley repeated a version of a line she has been using as a candidate that seems to allude to Mr Trump and his political career as replete with controversies. “It’s time for a new-generation leader. We’ve got to leave the baggage of the negativity behind,” she said. Meanwhile, Mr Trump in Iowa earlier this week attacked the Florida governor as an enemy of corn-based ethanol in his largest campaign event in the state. The former president spoke to more than 1,000 Iowans and Nebraskans packed into the event hall inside Mid-America Center. Mr Trump declared himself “the most pro-farmer president that you’ve ever had” at the event, which was aimed at promoting his administration’s agricultural record. “I fought for Iowa ethanol like no president in history,” he said. Read More Trump and DeSantis begin eyeing Super Tuesday states as they prepare for 2024 long game Trump says ‘damaged’ DeSantis is ‘desperately trying to get out’ of 2024 race Trump lawyer Alina Habba leaves his defence team in New York fraud case Mexico's president breaks with tradition in quarrel with scrappy opposition upstart A competitive race for an open House seat is taking shape in a Michigan battleground district Trump wanted to tap phones of White House aides, new book claims