There are public figures about whom so much ink has been spilled that it seems unlikely anything new or interesting could be said. I assumed Sarah Palin was one of those people when I started reporting my new book, Insurgency: How Republicans Lost Their Party and Got Everything They Ever Wanted.

Palin has been glossed over or edited out of many journalistic accounts that have attempted to take stock of a Republican Party so completely and thoroughly dominated by former president Donald Trump. Trump, by the sheer force of his compulsive need for affirmation, almost demands it be so.

But as unwilling as Trump was to say much to me about the ways Palin or others shaped his own political development—and she most certainly did, as I would discover—it soon became clear to me that you couldn’t tell the story of how the G.O.P. gave way to Trump without the backstory of Alaska’s former governor. And there was a lot to tell.

Storm in a Tea Party

Trump’s own pollster, Tony Fabrizio, described Palin to me as “the tip of the spear,” meaning that Fabrizio saw in her a vehicle for the anger and resentment that would manifest itself in the Tea Party before it fueled the Trump movement. I learned that Fabrizio was one of several future Trump advisers who saw such a spark in Palin early on that they were interested in seeing if she would run for president in 2012.

Ultimately, Fabrizio didn’t participate in a pivotal meeting between Palin and several other future Trump strategists in early 2011 that showed how serious some conservatives were about her leading their party. But Stephen K. Bannon did, joining the conservative author Peter Schweizer and the veteran right-wing activist David Bossie at the Four Seasons in Scottsdale to make their case to Palin directly that she had a serious shot at becoming the G.O.P. nominee that year.

Donald Trump’s pollster, Tony Fabrizio, saw in Sarah Palin a vehicle for the anger and resentment that would manifest itself in the Tea Party before it fueled the Trump movement.

As I report in the book, Palin seemed to have serious misgivings about another national campaign that would keep her on the road for long stretches away from her family in Alaska. But even as she expressed these private doubts, she was stringing the rest of us along, making a jaunt up the East Coast on Memorial Day weekend during which she stopped for selfies at Gettysburg and almost upstaged Mitt Romney as he announced his own campaign in New Hampshire.

Crucially, that was the same trip on which she also met Trump for a bite of pizza (he used a fork, infamously) near Trump Tower. “Don’t think he wasn’t watching,” Fabrizio told me. Like many of the opinions Trump would form of American politics and conservatives, his views were shaped by Fox News, where Palin was making $1 million a year as a contributor. He saw she had something, and he wanted to size her up in person.

She never ran for president. But earlier this month she announced she’s running for Congress in Alaska after a decade-long hiatus from political life. Those were years when she and many of us would begin to see how she was in fact the progenitor of Trumpism, not just a vessel for the grievances of future Trump voters but someone who understood them better because she had lived them herself.

Trump saw Palin had something, and he wanted to size her up in person.

One of the most revealing pieces of reporting I came across was an incident from early in her political career in Alaska.

The son of a scion of state G.O.P. politics had been caught on e-mail indiscreetly calling someone who was one of Palin’s neighbors “valley trash,” a reference to the area they lived in near Anchorage known as the Mat-Su Valley.

Palin leaned into it. She sported a T-shirt that said, Proud to be Valley Trash and posed for a photo. I’ve seen the headlines that say Republicans have “moved on,” and that she doesn’t stand a chance. Maybe.

Sound familiar?

Jeremy W. Peters is a correspondent for The New York Times who covers media and politics. His new book, Insurgency: How Republicans Lost Their Party and Got Everything They Ever Wanted, is out now from Crown