This week’s debate over his very eligibility for office served as a stark reminder that anyone else facing such a wide array of legal problems would have left the political stage long ago.In another era, a politician would have walked away.For decades, American elected officials facing criminal charges or grave violations of the public trust would yield their positions of power, if only reluctantly, citing a duty to save the country from embarrassment and ease the strain on its institutions.Then came Donald J. Trump. The former president isn’t just forging ahead despite four indictments and 91 felony charges, but actively orchestrating a head-on collision between the nation’s political and legal systems.The ramifications continued to accrue this week, when the fundamental question of the former president’s eligibility for office was all but forced upon a Supreme Court already mired in unprecedented questions surrounding Mr. Trump’s plot to overturn the 2020 election.But the heated legal debate over whether Mr. Trump engaged in an insurrection obscured the extraordinary reality that he is running for president at all — returning with fresh vengeance and a familiar playbook built around the notions that he can never lose, will never be convicted and will never really go away.That blueprint remains intact largely because his approach continues to yield political returns.Far from agonizing over the collateral damage from his never-surrender ethos, Mr. Trump seems incentivized by strife, tightly braiding his legal defense with his presidential campaign. He has tried to run out the clock on his criminal trials, a strategy that earned a new victory on Friday when the Supreme Court declined to decide a key point of contention in his federal 2020 election case immediately.While this year began with most Republicans telling pollsters that they preferred a different presidential nominee, the calendar will flip to 2024 with roughly two-thirds of the party aligned behind Mr. Trump. His legal problems, which in decades past would have bolstered rivals for a major party’s presidential nomination, have only caused Republican voters to unify around him more.“This has been the mystery of the Trump era — every time we think this is the final straw, it turns into a steel beam that merely solidifies his political infrastructure,” said Eliot Spitzer, a former Democratic governor of New York. Mr. Spitzer resigned as governor in 2008 amid a prostitution scandal, saying at the time that he owed as much to his family and the public.Lately, Mr. Trump has faced increased criticism that he is adopting fascist language and authoritarian tactics. Defending himself, he insisted repeatedly this week that he had never read “Mein Kampf,” Adolf Hitler’s Nazi manifesto.Of course, if there were a guidebook on how to run traditional American political campaigns, he would not have read that, either.At the start of his 2016 bid, he disparaged decorated military veterans, and voters looked past it. When a hot-mic recording surfaced of Mr. Trump casually claiming that celebrity status made it easier to sexually assault women, he resisted calls from fellow Republicans to step aside, dismissed the remarks as “locker room talk” and, 32 days later, won the presidency.The cycle repeated itself for years, leading to a kind of truism inside Trump world that the swirl of chaos and coup de théâtre surrounding the former president was almost always surprising, but hardly ever shocking.The absurdity of it all, in other words, always seemed to make perfect sense.Mr. Trump and his allies have sought to turn his impeachments into a political strength. Rebecca Noble for The New York TimesEven the riot by Mr. Trump’s supporters at the Capitol nearly three years ago adhered to that adage. Whether the attack was the ultimate coda to his presidency or the beginning of a darker phase in U.S. politics, the violence, in hindsight, was as horrifying as it was foreseeable.Mr. Trump, after all, had spent four years wielding the powerful White House bully pulpit to insist that any critical news coverage was a lie, that no elected official he opposed should be believed and that the courts could not be trusted.The story in Washington again unfolded in ways that were surprising — but hardly shocking. Days after Mr. Trump left office, polls showed that he maintained high levels of support inside his party. House Republicans who had voted to impeach him found themselves the targets of censure and primary challenges. Republican leaders visited him at Mar-a-Lago — a steady stream of supplicants bowing before their exiled king.It soon became clear that the Republican Party’s best opportunity to cast Mr. Trump aside had passed when 43 of its senators voted to acquit him in his impeachment trial after the Capitol riot.In an interview last month, Mr. Trump all but bragged about continuing his latest presidential campaign despite his criminal charges.“Other people, if they ever got indicted, they’re out of politics,” he told Univision. “They go to the microphone. They say, ‘I’m going to spend the rest of my life, you know, clearing my name. I’m going to spend the rest of my life with my family.’”“I’ve seen it hundreds of times,” Mr. Trump said, concluding that such decisions were always mistakes. “I can tell, you know, it’s backfired on them.”Mr. Trump’s legal problems, which in decades past would have bolstered rivals for a major party’s presidential nomination, have only caused Republican voters to unify around him more.Max Whittaker for The New York TimesMr. Trump’s commitment to the fight is rooted in a “preoccupation with not being seen as a loser,” said Mark Sanford, the former Republican governor of South Carolina, who considered stepping down as governor in 2009 when an extramarital affair erupted in scandalous national headlines.He ultimately remained in office, recalling in an interview this week that he had wanted to take responsibility for his actions and had hoped his regret and humility would serve as an example to his four sons and lead to a reconciliation with his constituents.Mr. Sanford said he doubted Mr. Trump had ever considered not running again.“For him to think about what’s best for the republic would mean having a frontal lobotomy,” Mr. Sanford said. “From the number of people he’s sued over the years to the number of subcontractors he’s ripped off to all of his bankruptcies, he has just bullied his way through life. He plays to an audience of one, and it’s not God — it’s Donald Trump.”Former Senator Trent Lott, a Mississippi Republican, said he would advise Mr. Trump to end his presidential campaign if one of the former president’s federal cases resulted in a felony conviction.Mr. Lott, a former Senate majority leader, was forced out of his leadership position in 2002 after praising Strom Thurmond, a longtime senator and ardent segregationist who died the next year.“At some point, someone has to say to him that he has to do what’s in the best interest of the country and shut down his campaign,” Mr. Lott said of Mr. Trump. “But I don’t see any indication so far that he plans on going anywhere but back to the White House.” More