The last time Donald J. Trump participated in competitive Iowa caucuses, he lost narrowly, accused Senator Ted Cruz of Texas of stealing the contest, claimed fraud, demanded that Iowa Republicans nullify the results, and called for a rerun.While Iowa has a history of troubles with its caucus results, there’s been no evidence of fraud. The 2016 Republican contest was, in fact, the only one since 2008 that had gone off without a hitch.And yet if Monday night ends with Mr. Trump underperforming expectations, both his history and his rhetoric during this year’s campaign suggest he won’t hesitate to cry foul and refuse to accept the result.Mr. Trump has already accused Gov. Ron DeSantis of Florida of “trying to rig” the caucuses. Laura Loomer, a far-right and anti-Muslim activist whom Mr. Trump last year considered hiring for a campaign post, suggested on social media that “the deep state” was engaging in “weather manipulation” to instigate Iowa’s Friday snowstorm and subzero temperatures to depress Trump turnout on Monday. And Donald Trump Jr. suggested in a Telegram video that “we can’t take anything for granted, or assume that everything is going to be on the up and up. We’ve seen this rodeo before.”Those claims are not likely to be met with much support from Iowa Republicans and the party volunteers who will operate the 1,657 caucus sites across the state.“If Trump says it’s fraud, he’s full of crap,” said A.J. Spiker, a former chairman of the Republican Party of Iowa who is backing Mr. DeSantis.Still, Iowa Republicans aim to protect themselves from campaigns claiming foul play at the caucuses.At each site, caucusgoers mark their presidential preferences on paper slips. Those slips are then counted in full view of whoever wants to watch. Typically a representative from each campaign watches the counting, and recording is allowed.“It’s the most transparent straw vote you could possibly do,” Mr. Spiker said.The Trump campaign’s headquarters in Urbandale, Iowa, on Saturday.Jon Cherry for The New York TimesMr. Trump’s pre-emptive Iowa fraud claims last month followed a flub by Mr. DeSantis’s wife, Casey DeSantis. She called on supporters to “descend upon the state of Iowa to be a part of the caucus.”“You do not have to be a resident of Iowa to be able to participate in the caucus,” she said.That earned Ms. DeSantis a rebuke from the state Republican Party.Only Iowans can participate in the caucuses. Republican volunteers are supposed to check for photo identification at the caucus sites. Still, Mr. Trump’s campaign suggested then that the DeSantis campaign had professed a “plot to rig the caucus through fraud.”Another candidate who has trafficked in conspiracies and has been sowing doubt about Iowa’s caucuses is Vivek Ramaswamy, who failed to qualify for recent debates.“The mainstream media is trying to rig the Iowa G.O.P. caucus in favor of the corporate candidates who they can control,” Mr. Ramaswamy said in a campaign video this week. “Don’t fall for their trick. They don’t want you to hear from me about the truth.”Voting rights groups and disinformation experts say the pre-emptive cries about fraud and rigged elections have become something of a new normal.“This follows the general playbook, the election denier playbook of just pre-emptively laying the groundwork for claims of fraud in the event of a loss,” said Emma Steiner, the Information Accountability Project Manager at Common Cause, a left-leaning voting rights organization. “It’s sort of future-proofing.”Indeed, Mr. Trump has long trumpeted baseless claims of fraud or rigging before an election. In 2016, weeks before Election Day, Mr. Trump started questioning the veracity of mail ballots in Colorado, citing little evidence. After he won the 2016 election, Mr. Trump claimed that widespread fraud cost him the popular vote (it did not), and he launched a commission to investigate voter fraud in the country (it folded without any significant findings).The Trump team has called elections rigged even when he is not participating in them. When the 2020 Democratic caucuses melted down because of a faulty app and a disorganized state party, Mr. Trump’s campaign questioned whether the results were “being rigged against Bernie Sanders.” His sons went further.“Mark my words, they are rigging this thing,” Eric Trump wrote on Twitter the night of the 2020 caucuses. “What a mess.” More