Removing a white face mask as she took the witness stand behind a Plexiglass shield, Sarah Palin likened herself to the biblical David taking on the mighty Goliath of American media, the New York Times newspaper.

The 58-year-old’s appearance in a Manhattan courtroom this week was a far cry from her heyday on the campaign trail, whipping up crowds with incendiary rhetoric as a US vice-presidential candidate in 2008.

But in making her pitch to a jury – the only nine voters who matter this time – Palin still had a star power, and reflex for bashing the media, that served as a reminder of how she paved the populist way for Donald Trump.

And when the former governor of Alaska was asked whether she might run for office again, she teased a back-to-the-future scenario for the Republican party and America. “The door’s always open,” she told the court.

Anyone wondering, “Whatever happened to Sarah Palin?” has not been paying attention to headlines of late. She declared that she would get the coronavirus vaccine “over my dead body”, duly tested positive for Covid-19 and went dining out in New York anyway, flouting public health guidelines.

The infection did cause a delay in her defamation trial against the New York Times, which published a 2017 editorial that incorrectly linked Palin to a mass shooting six years earlier (it corrected the editorial the following day but she contends that the correction did not go far enough).

Once the trial got under way, Palin told jurors she was “mortified” by the mistake and called the Times “the be-all, end-all, the loud voice in American media”. She said: “It was devastating to read a false accusation that I had anything to do with murder. I felt powerless – that I was up against Goliath. The people were David. I was David.”

But she faces an uphill battle against a paper that has not lost a defamation case in more than half a century. She must convince jurors that the Times acted with “actual malice”, meaning that it knew the editorial was false or had reckless disregard for the truth.

The court has heard Palin – she and husband Todd divorced in 2020 after 31 years – describe herself as a single mother and grandmother who “holds down the fort” for her family in Alaska when not advising candidates about “the good, bad and ugly” of politics. She also recalled the surprise over her eruption on the national political stage in 2008, saying: “I don’t think they were prepared for me.”

That is an understatement. Palin was a wildly improbable choice back then as running mate for Republican John McCain in the contest with Democrat Barack Obama, bidding to become the first Black president, and his running mate, Joe Biden.

The ascent of Palin – going outside what had been deemed an acceptable talent pool in terms of experience and judgment – is now seen as a pivotal moment in American political history, opening a Pandora’s box of divisive, nativist, anti-intellectual, celebrity-driven smash-mouth politics.

Steve Schmidt, then a senior adviser to the McCain campaign, was the first to float the idea of Palin as running mate. In an interview with the Guardian, Schmidt said his exact words were: “We should take a look at Sarah Palin. I don’t know a lot about her other than she’s the most popular governor in the country with an 87% approval level.”

So it was that in August 2008 McCain invited Palin to his ranch in Sedona, Arizona, to consider the bold move. Schmidt recalled: “Mark Salter [another adviser] and I are there with McCain, and McCain says, ‘Come on, boys, let’s go talk to her.’

“I said to him, ‘It’s completely inappropriate for us to be in this meeting. This is a presidential-level decision. Only you can make the determination she’s prepared to take the 35-word oath and become president.’”

So Schmidt and Salter did not attend. “The singularly greatest regret of my life,” Schmidt acknowledged this week. “It’s the dumbest thing I’ve ever done.”

He is convinced that, had they been in the room, they would have immediately realized how unprepared and unqualified Palin was and done everything in their power to talk McCain out of it.

“No one will ever know what the discussion was,” continued Schmidt, a co-founder of the anti-Trump Lincoln Project. “There were two people in the room: him and her. I’m fairly certain if there was a substantive conversation that I was party to I would’ve chained myself to the back of the bumper to stop her from being announced.

“I’ve never encountered a person and I’ve never experienced in my political career someone so abjectly dishonest. You could not get a straight answer on a question on the most basic informational level, which was my initial warning sign about her in the hours after McCain picked her.”

McCain’s impulsive and fateful decision – for which he later expressed regret – is chronicled in a new book, Insurgency: How Republicans Lost Their Party and Got Everything They Ever Wanted, by Jeremy Peters. He writes: “McCain turned to his wife, Cindy. ‘John, it’s a gamble,’ she said.

“This made McCain’s face light up. ‘Well, I wish you hadn’t said that,’ he said. McCain, an avid craps player, balled up his fist and blew on it, then shook it like he was about to roll a pair of dice. ‘Fuck it,’ he said. ‘Let’s do it.’”

The gamble backfired as McCain still lost the election and, in the eyes of critics, tainted his legacy by accelerating the Trumpification of the Republican party. During the campaign Palin’s ignorance became clear as she stumbled over basic questions such as what newspapers and magazines she read.

She accused Obama of “palling around with terrorists” and used the term “shuck and jive” to portray him as evasive and dishonest. (She later wrote on Facebook: “For the record, there was nothing remotely racist in my use of the phrase ‘shuck and jive’.”)

Peters, a journalist at the New York Times, said in an interview: “She is the tip of the spear for Donald Trump and everything he unleashed in American politics. Like Trump, her appeal to her supporters was as much about who her perceived enemies were and as it was about her herself.

“She also had a really intuitive sense of how to go into combat with those enemies, especially the media. She was the canary in the coalmine when it came to doing lasting damage to the reputation of the mainstream media, which had already been taking a beating but had never been made into a real political enemy to the extent it would be under under Trump.”

Palin’s loose talk of the media “making things up” and claims that it should “quit lying” foreshadowed Trump’s popularisation of phrases such as “‘enemy of the people” and “fake news”.

Peters added: “She also had a real sense for social media and using that to basically say whatever she wanted and get attention that wouldn’t require her to go to the mainstream media, because the mainstream media would then just cover whatever she said on Facebook.”

Palin went on to campaign for the Tea Party, a conservative revolt fuelled by rage against elites, distrust in government and racial hostility to Obama. It was another harbinger of the “Make America Great Again” white grievance movement.

Palin had a five-year stint as a contributor to the conservative Fox News channel on a reported $1m contract, endorsed Trump for president and, emulating his past career as a reality TV star, made a surprise appearance on The Masked Singer, rapping and dancing in a pink bear costume.

Now, should she pull off an unlikely legal victory over his old foe the New York Times – a judgment that could have a chilling effect on freedom of the press – Trump would probably be the first to congratulate her. What he may never grasp is the political debt he owes her.

Larry Jacobs, director of the Center for the Study of Politics and Governance at the University of Minnesota, said: “Would there be a Donald Trump without Sarah Palin? It’s hard to imagine Trump coming out of nowhere. Sarah Palin paved the way for Donald Trump.”

Last year Palin hinted at an Alaska Senate run against Republican moderate Lisa Murkowski. If Trump regains the White House in 2024, she might find another comeback path. Jacobs admitted: “I find it impossible to make predictions about a Republican party that has veered so far to the extreme, so far towards irresponsibility.

“This is a party without a measure of itself. It’s a chaotic party that no longer has core principles so yes, I could see Palin ending up in the cabinet if she were able to rehabilitate herself and find a way to become relevant again.”