Several weeks after the 2020 election, as Donald J. Trump worked to overturn his defeat, he called a Republican lawmaker in Michigan with an urgent request. Mr. Trump had seen a report that made wild claims about rigged voting machines in a rural northern county in the state. He wanted his allies to look into it.The president told the lawmaker that a Michigan lawyer, Matthew DePerno, had already filed a lawsuit and that it looked promising, according to the lawmaker and two others familiar with the call.For that lawmaker, the lawyer’s name set off alarms. Mr. DePerno, a trial attorney from Kalamazoo, was well known in the Legislature for representing a former legislator embroiled in a sex scandal. Mr. DePerno had spent years unsuccessfully accusing lawmakers and aides of devising a complex plot to bring down his client, complete with accusations of collusion, stalking, extortion, doctored recordings and secretive phone tapping. Federal judges dismissed the cases, with one calling a conspiracy claim “patently absurd.”Mr. DePerno’s involvement will only undermine your cause, the lawmaker, who along with the others asked for anonymity to discuss the private conversation, told the president. Mr. Trump seemed to dig in: If everyone hates Mr. DePerno, he should be on my team, Mr. Trump responded, according to two of the people.Donald Trump endorsed the candidacy of Matthew DePerno, who pushed a conspiracy theory about the vote count in a rural Michigan county.Emily Elconin/ReutersBolstered by his association with the former president, Mr. DePerno on Saturday was nominated as the G.O.P. candidate for attorney general, the top legal official in the state, at a state party convention. He is among a coterie of election deniers running for offices that have significant authority over elections, worrying some election experts, Democrats and some Republicans across the country.This month, the Michigan attorney general’s office released documents that suggest Mr. DePerno was a key orchestrator of a separate plot to gain improper access to voting machines in three other Michigan counties. The attorney general, Dana Nessel, the Democrat Mr. DePerno is challenging for the office, requested that a special prosecutor be appointed to pursue the investigation into the scheme and weigh criminal charges. Mr. DePerno denies the allegations and called them politically motivated.Mr. DePerno played a critical role in the report mentioned by Mr. Trump about that rural county, Antrim. The report turned a minor clerical error into a major conspiracy theory, and was later dismissed as “idiotic” by William P. Barr, an attorney general under Mr. Trump, and “demonstrably false” by Republicans in the Michigan Senate.For some who have watched his career, there are parallels between Mr. DePerno’s dive into election conspiracies and his recent legal record. He has at times used the legal system to advance specious claims and unfounded allegations detailed in a blizzard of lengthy filings, according to an examination of court records in some of his cases and interviews with attorneys and judges.“The playbook is the same,” said Joshua Cline, a former Republican legislative aide whom Mr. DePerno sued as part of the conspiracy allegations involving the legislature. The case was dismissed in court. “It’s trying to play to a base of people and trying to get them to buy into something that when you put the magnifying glass to it, it falls apart,” Mr. Cline said. “It’s more than terrifying.”More Coverage of the 2022 Midterm ElectionsThe Evidence Against a Red Wave: Since the fall of Roe v. Wade, it’s increasingly hard to see the once-clear signs of a Republican advantage. A strong Democratic showing in a special election in New York’s Hudson Valley is the latest example.New Women Voters: The number of women signing up to vote surged in some states after Roe was overturned, particularly in states where abortion rights are at risk.Sensing a Shift: Abortion rights, falling gas prices, legislative victories and Donald J. Trump’s re-emergence have Democrats dreaming again that they just might keep control of Congress. But the House map still favors Republicans.Bruising Fights in N.Y.: A string of ugly primaries played out across the state, as Democrats and Republicans fought over rival personalities and the ideological direction of their parties.Mr. DePerno declined to be interviewed. In response to written questions, he stood by his claims and defended his legal tactics.“If you are criticizing me on being a bulldog of a lawyer who is well-versed in the law and procedure and who defends his client to the best of his ability, I take that criticism with pride,” he said in a statement.At least five times, Mr. DePerno’s clients or legal colleagues have asked Michigan’s Attorney Grievance Commission to investigate his conduct, according to records reviewed by The New York Times. Three requests have not been previously reported: The commission keeps the filings and investigations private unless they result in formal disciplinary complaints.Three of the five investigations were closed without disciplinary actions, the records showed. In at least one of those closed cases, however, the commission did find Mr. DePerno’s conduct — baselessly accusing a judge of taking a bribe — worthy of a private “admonishment,” according to a 2021 letter viewed by The Times. Mr. DePerno said a fourth inquiry, regarding the Michigan Legislature cases, also closed privately, and another, related to the Antrim County case, is still open. Mr. DePerno did not respond to a request for records confirming his account.Asked about the grievances, Mr. DePerno said: “I have never been disciplined. The reality is that any person at any time can file any garbage they want” with the commission.One of the completed investigations involved former clients who sued Mr. DePerno over malpractice, claiming he had taken actions without their consent, overcharged them and tried to foreclose on their home as payment. A federal magistrate judge also expressed concerns about Mr. DePerno’s conduct in the case, at one point sanctioning him for obstructing a deposition and coaching a witness. In the same hearing, the judge also said Mr. DePerno had “arrogantly tried to justify the unjustifiable” in a brief, and falsely and unethically accused another lawyer of being unprofessional.“Mr. DePerno, you get an F,” U.S. Magistrate Judge Joseph G. Scoville said, according to a transcript.Mr. DePerno called the federal magistrate’s comments “overly harsh and unwarranted.” The malpractice lawsuit, which was first reported by Bridge Michigan, was later settled.A Scandal in the State HouseMr. DePerno also faced criticism in a far more prominent case. In 2015, he was hired by Todd Courser, a freshman state House member and Tea Party activist who was accused of trying to cover up an extramarital affair with a fellow legislator by producing a “false-flag” email, according to court filings and articles in The Detroit News.Mr. DePerno called in forensic experts to argue that audio recordings used by local media in reporting on the scandal had been doctored. He claimed that legislative leaders and aides had conspired to wiretap Mr. Courser and fabricate and destroy evidence. He lodged accusations of lying and bias against the lawyers and judges. He sued aides, lawmakers, The Detroit News, the Michigan State Police, the attorney general and even the hotel chain where Mr. Courser and the other lawmaker met.The legal blitz was not successful. Some claims were dismissed for procedural reasons; others were found to have no merit. One federal district judge, Gordon Quist, called the conspiracy claim “not only implausible, but absurd on its face.” Judge Quist did reject a request to sanction Mr. Courser and Mr. DePerno for filing claims with no basis in fact. An appeals court ruling also noted that one of his theories was “not entirely implausible,” but still found there was no merit to that claim.Another federal appeals court panel wrote that Mr. Courser spent “more time enumerating claims than developing arguments.”Mr. DePerno, left, with Todd Courser during a hearing in 2016. Mr. Courser was accused of trying to cover up an extramarital affair with a fellow legislator.David Eggert/Associated PressA state circuit court judge imposed a nearly $80,000 sanction against Mr. DePerno and Mr. Courser in a defamation lawsuit against The Detroit News, finding Mr. DePerno “does not have a reasonable basis that the underlying facts are true as represented,” according to a transcript of a state court hearing in 2019. Mr. DePerno later sued that judge in federal court, accusing him of bias. He eventually dropped the case against the judge and agreed to a settlement with the news organization that cut the payment to $20,000.The Courser cases became a legal morass, with criminal charges filed against Mr. Courser and a barrage of civil suits. The cases dragged on for years, exasperating lawyers and clients. Michael Nichols, a Michigan lawyer who represented a co-defendant in a related criminal case, said Mr. DePerno often seemed to be more interested in pushing his theory about political bias against Tea Party-aligned Republicans than defending his client against the criminal charges.“I think he wanted to make this all about getting attention as the doll of the Tea Party movement,” Mr. Nichols said.In August 2019, Mr. Courser pleaded no contest to willful neglect of duty by a public officer, a misdemeanor.Mr. Courser in a recent interview stood by his longtime contention that he is the victim of a conspiracy by the legislative aides, legislators and others.He said Mr. DePerno “did everything he had to do to defend his client against the tyranny and unjust prosecution.”“I have nothing but great praise and admiration,” Mr. Courser said. “He’s going to be a great attorney general.”2020 Election ClaimsShortly after Mr. Trump lost the presidential election in Michigan, Bill Bailey, a real estate agent in the state’s lower peninsula, noticed some anomalies in the initial vote count from his local county, Antrim.The results in the conservative county had suddenly, and briefly, been reported as a win for Joseph R. Biden Jr., owing to an error in the clerk’s office. Mr. Bailey connected with Mr. Trump’s legal team, which advised him to get a Michigan lawyer, according to an associate of the legal team.He found Mr. DePerno, who got a court order granting him access to data from Antrim County’s voting machines. That information became the basis for the Antrim report and also gave Mr. DePerno a place in the loose collection of Trump associates, self-proclaimed data gurus and lawyers who were searching for evidence that could propel the fiction that Mr. Trump won the race. Mr. DePerno, along with the others, have continued that quest.Mr. DePerno in October 2021, at an event calling for an “audit” of the 2020 election in Michigan, which Mr. Trump lost.Matthew Dae Smith/Lansing State Journal, via Associated PressAs his work in Antrim County gained national attention, he began raising money. By December 2020, Mr. DePerno had set up multiple donation links on his website under the banner of “The 2020 Election Fraud Defense Fund.” One was hosted by a Michigan resident and has raised $62,000 to date. Another was started by Mr. DePerno, and has raised more than $400,000, according to a live tracker on the site.Mr. DePerno eventually added a direct PayPal invoice button urging people to “Donate via PayPal.” The link went directly to his law firm’s website. Asked about the PayPal link, Mr. DePerno said it was meant for clients to pay their legal bills.Mr. DePerno has refused to answer further questions about how he has used the money. In June, Republicans in the State Senate asked the attorney general to investigate how people have used the Antrim County theory “to raise money or publicity for their own ends,” though they did not single out Mr. DePerno.By spring, as it became clear that Mr. DePerno was flirting with a run for attorney general, Republicans in Michigan grew fearful that his candidacy could be a drag on the entire ticket, according to multiple former members of the state party and others familiar with the state party discussions. They encouraged another Republican to run and tried — and failed — to head off a potential endorsement from Mr. Trump.In September, Mr. Trump issued an endorsement praising Mr. DePerno for being “on the front lines pursuing fair and accurate elections, as he relentlessly fights to reveal the truth.”Kitty Bennett More