LONELINESS is a potent force in politics. “I didn’t leave the Democratic Party. The Democratic Party left me,” Ronald Reagan liked to say, recalling why he became a Republican in his 50s. This week it was the turn of Paul Ryan, the Speaker of the House of Representatives, to explain why he will retire from Congress at the next election in November. Mr Ryan, a former vice-presidential nominee, talked of his three teenage children and of his own father’s early death, and noted that if he served another term in Washington, his children “will only have known me as a weekend dad.” He was surely sincere. Visit Janesville, his hometown in the dairylands of southern Wisconsin, and even Democratic-voting neighbours attest to Mr Ryan’s love of family, whether escorting his brood to church or taking his daughter on a first deer hunt.

But Mr Ryan left unsaid the other way in which his Speakership leaves him painfully alone. Still only 48, he was the future of the Republican Party once: a champion of a flinty yet compassionate conservatism admired by both rank-and-file members of Congress and deep-pocketed donors. Paul Ryan’s Republican Party cast government debt as both worrying and wicked: a betrayal of the next generation of Americans. It backed free trade and praised immigrants for their work ethic. Mr Ryan spent years telling rank-and-file conservatives that their dislike of government welfare was not mean-spirited but kindly. Delegates at the Republican National Convention in 2012 cheered when he accused Democrats of offering “a dull, adventureless journey from one entitlement to the next, a government-planned life, a country where everything is free but us.” Above all, Mr Ryan stood for a credo that America is “the only nation founded on an idea, not an identity”. That idea, he would explain with a catch in his voice, is the notion that the condition of your birth should not determine the outcome of your life.

That is not the Republican Party of President Donald Trump, a man not even mentioned in Mr Ryan’s retirement statement. Mr Trump scorns conservative ideas and won office by embracing identity politics. As president the former reality TV star has continued to demonstrate that what a Republican does matters less than whom they are for, or more important still, whom they are against. Mr Trump enjoys 89% approval ratings among Republicans, despite a string of unfulfilled campaign promises, because he is a fighter who makes liberals mad, appals hoity-toity intellectuals and frightens foreigners.

To quote Senator Bob Corker of Tennessee, another Republican retiring this year, grassroots support for the president is “more than strong, it’s tribal”. When colleagues meet Republicans on the campaign trail, “they don’t care about issues, they want to know if you’re with Trump.”

Mr Trump worries greatly about where people were born, attacking a federal judge as “very bad” and a “hater of Donald Trump” during the presidential election campaign of 2016, citing the judge’s Mexican ancestry—a charge that Mr Ryan at the time called “the textbook definition” of racism. Mr Trump is blithe about debts and deficits, insisting that tax cuts passed in 2017 will pay for themselves. Unlike Mr Ryan, who calls reforming government support schemes the biggest task facing Republicans today, Mr Trump has ordered aides to leave untouched Social Security and Medicare, pension and health benefits mostly paid to the old, who constitute a core Trump constituency. In 2016 Mr Ryan urged congressional interns to practice civil politics. By all means disagree with opponents’ ideas, he told them, but do not question their motives or patriotism.

Mr Trump calls the FBI a corrupt "deep state" and says the Democrats want drugs and murderous migrants to "pour into our country". Mr Ryan’s response is retreat, it turns out. To adapt Reagan’s words for a bleaker age, the Republican Party left Paul Ryan, so he is leaving politics. A former Republican leadership staffer predicts that the Speaker will take refuge in the world of conservative ideas. As word of his retirement spread, Washington rumours wondered if he might become the next head of the American Enterprise Institute, a think-tank. Perhaps in 15 or 20 years Mr Ryan may return to politics, suggests the former staffer, a bit wistfully.

Peter Wehner of the Ethics and Public Policy Centre, a long-time Ryan colleague and friend, notes that the Speaker is now free of both the “adult daycare” role of supervising an intemperate president and from worries about mid-term elections, which look grim for House Republicans. In the meantime, Mr Wehner sighs, “It is Trump’s party,” more clearly than ever.