Younger Americans are decidedly more liberal than their parents. On election day 2022 they thwarted a ballyhooed “red wave”, saved the Georgia senator Raphael Warnock from defeat and deflated Kari Lake’s bid for Arizona governor. Nationally, voters under 30 went Democratic 63-35.

Millennials, those born between 1981 and 1996, and members of Generation Z, born between 1997 and 2012, are also less than proud of living in the US, according to survey data. Suffice to say, “Maga” sloganeering leaves them less than reassured.

Those generations grew up in the shadows of 9/11, the Iraq war, the great recession and Covid. Their school lunch menus featured shooter lockdown drills. They are ethnically diverse. Millennials have defied political expectations. They did not shift right with age. Instead, they make Republicans sweat.

Along with race, gender and culture, inter-generational rivalry can be tossed into that long-simmering pile of resentments known as America’s cold civil war. Enter Philip Bump and his first book, aptly subtitled The Last Days of the Baby Boom and the Future of Power in America. Bump is a national columnist for the Washington Post. Demographics, culture and economics are part of his remit. Through that prism, The Aftermath delivers.

Bump attempts to explain how the US reached its present inflection point and offers a glimpse of what may come next. His tone is methodical, not alarmist.

Gently, he introduces the reader to the term “pig in the python”, coined by Landon Jones, once managing editor of People magazine, to describe the demographic bulge created by GIs who returned from the second world war. Bump pays respect to Jones’s book, Great Expectations, which stands among the “first serious examinations of the baby boom”. Hence the label Baby Boomers, for people born in those fertile post-war years.

Boomer politicians include Bill Clinton, George W Bush, Donald Trump and Newt Gingrich. They may not have made the world a better place but they definitely left their mark. Their appetites frequently eclipsed their judgment. Clinton and Trump were impeached. Both faced lawsuits alleging sexual assault. Gingrich was forced out as House speaker.

“They are a generational tyranny,” Bump quotes Jones.

“OK Boomer” is a catchphrase and retort, not a compliment.

More than three decades ago, Lee Atwater, the manager of George HW Bush’s 1988 presidential campaign, believed the boomer experience provided a more cohesive political glue than income, political tradition or religion.

“This group has dominated American culture in one form or another since it came into being,” he observed.

Stratocaster in hand, Atwater played with Ronnie Wood of the Rolling Stones at Bush’s inauguration. The new president jammed along on air guitar. Atwater recorded an album with BB King and others. Now, Atwater, Bush, King and Charlie Watts are gone. Wood, Mick Jagger and Keith Richards play on. There’s always time for one more tour, until there isn’t.

Bump also addresses tensions within the Democrats’ diverse, upstairs-downstairs coalition, observing that race and ethnicity are not necessarily destiny. Among minority voters without college degrees, the party of FDR and JFK has ceded ground to the GOP. The much-vaunted “coalition of the ascendant” has not lived up to its hype.

Bump notes divides between Black and Latino voters. In the 2020 primaries, Black Democrats sided with Joe Biden, Latinos with Bernie Sanders. Among Latinos, Trump ran three points better against Biden than against Hillary Clinton. Among Black voters, he was five points better.

As with working-class whites, cultural issues retained their salience for those without a degree. Before the supreme court gutted a woman’s right to choose, Republicans possessed the luxury of watching the Democrats trip over themselves as they grappled with the latest leftwing orthodoxy, turning off wide swaths of the electorate, including Boomers, as they did so.

Now it’s the Republicans’ turn to squirm. Voters in red Kansas and Kentucky rejected abortion bans. In the midterms, inflation and abortion were the two most important issues. Inflation may be receding but abortion is not going away.

As Bump observes, women older than 60 frequently emerged as both faces of the resistance to Trump and a moderating force. More than three in five Americans are angry or dissatisfied with the supreme court decision on abortion, yet the GOP faithful demands self-immolation.

Affirmative action provides another example of ethnic fluidity. In 1996, California adopted Proposition 196 and scrapped race-based preferences, despite overwhelming Latino opposition. As Bump describes it, the Latino share of the electorate was smaller than its proportion of the population. If results were weighted to reflect that larger figure, Proposition 196 would been defeated.

Priorities of ethnic blocs can change. By 2020, support for affirmative action among Californian Latinos appeared lukewarm at best. At the same time Californians were sending Biden to the White House they resoundingly rejected Proposition 16, an attempt to undo Proposition 196.

By the numbers, backers of Proposition 16 spent more than $31m for around 44% support. Opponents of the measure raised a meager $1.6m yet took 56%.

Bump posits that in the future, the US will look more like Florida: older and less white. Florida has moved right in recent years – whether ageing millennials and Gen Z-ers push it back towards the center remains, of course, to be seen. Bump also poses a series of “what ifs”, unanswered: “What happens if changes in the state reduce the motivation for Americans or immigrants to move there? What if the federal government further constrains international migration?”

“Florida’s future is dependent on decisions made in the present,” he writes. “The long term depends on the short term.”

• The Aftermath: The Last Days of the Baby Boom and the Future of Power in America is published in the US by Penguin Random House