Long before Fiona Hill arrived to testify on Capitol Hill, there was a long line for public seats and a crackling sense of anticipation for one of the most important moments so far in the impeachment of Donald Trump.

The occasion did not disappoint. It was an epic encounter about public service, loyalty, the founding ideals of the United States, foreign policy and the treatment of women. Hill, formerly the top Russia expert in the White House, emerged as a national heroine, for her mastery of facts and argument, and her coolness under pressure.

The six hours of speeches and interrogation were far from over when Republicans on the intelligence committee stopped trying to outwit her and poke holes in her testimony. They resorted to making statements rather than asking questions. Meanwhile, Twitter had fallen into a collective swoon.

She was deemed a “national treasure” by Politico’s congressional bureau chief, John Bresnahan. Nicolle Wallace, who worked in George W Bush’s White House declared: “I spent much of my career in politics. I’ve never seen anyone like Fiona Hill.”

George Conway – lawyer, leading Trump critic and husband of one of the president’s top advisers – declared he was starting a Fiona Hill fan club.

When Hill was senior director of the national security council (NSC), the president seems to have been only vaguely aware of her importance, mistaking her early on for a secretary. But that was not necessarily unusual. As Hill testified on Thursday, Trump also had no idea who his Ukraine adviser was.

Impeachment hearings: Sondland was ‘involved in domestic political errand’, Hill testifies – live Read more

Now the 54-year-old Hill, born in northern England, who had gone to work for Trump in the spirit of non-partisan public service, was emerging – unwillingly but inexorably – as his nemesis.

Even before she appeared at her first public hearing on Thursday, she was cast as a central figure in the impeachment saga, and not just because she was a witness to key events at the White House.

Many people saw in Hill an antithesis, if not a cure, to some of the toxins corroding her adopted nation. She walked into the committee room in the Longworth building of the House of Representatives, a woman before an almost all-male panel, cool and forensic at a time of partisan vitriol, an emissary from the world of scholarship cast into the midst of a battle in which facts are in danger of being defeated by manipulated opinion.

In her testimony on Thursday, Hill confirmed a story that had appeared in the press that when she was 11, a schoolboy set fire to her pigtails when she was sitting an exam. She doused the burning hair and finished the test. She joked that it led to a bowl haircut from her mother that left her looking like Richard III in her school photo. It also sounded like a metaphor for Thursday’s hearings.

Hill took her seat and the witness table alongside David Holmes, a US diplomat sucked into the maelstrom because he had been witness to a raucous phone conversation between Trump and one of his politically appointed ambassadors in a Kyiv restaurant.

Facebook Twitter Pinterest David Holmes and Fiona Hill on Capitol Hill. Photograph: Susan Walsh/AP

Both gave opening statements, but Hill’s immediately stood out for its bluntness, and for the personal history underlying it. She began by pointing out that she had become an American by choice and had come from the same part of north-east England as George Washington’s forefathers.

She grew up in County Durham in a family that “always struggled with poverty” and whose men had been coalminers through generations. Her own father, Alfred Hill, first went down the pit at the age of 14, to join his father, brother, uncles and cousins, digging Durham coal. Her mother, a midwife, still lives in Hill’s home town.

When coalmining died in Durham, Hill’s father wanted to immigrate to the US, but could not leave because his mother had been debilitated by a life of hard labour and he had to stay to care for her.

Alfred Hill lived long enough to see his daughter escape poverty, cross the Atlantic and rise to become one of the foremost experts on the Soviet Union and Russia in Washington.

Hill’s opening message to the two ranks of members of Congress arranged in front and above her was that she had come before them as the very embodiment of the American dream. Because of Britain’s enduring social rigidity, she had to emigrate for her talent and expertise to be valued properly.

“I grew up poor, with a very distinctive working-class accent,” she told the House intelligence committee in that same accent, somewhat softened now by her years in the US. “In England in the 1980s and 1990s, this would have impeded my professional advancement. This background has never set me back in America.”

She had served under three presidents, including in the role of national intelligence officer for Russia and Eurasia. She co-wrote a book on the Russian president called Mr Putin: Operative in Kremlin, which focuses on how his KGB mindset influences how he rules and how he conducts Russian foreign policy.

It was because of her mastery of her subject that she was asked to work in the White House in 2017. She decided to take the NSC job, despite the trepidation of some friends and colleagues, because she thought she could help with the official policy of the Trump administration, mend relations with Moscow as much as possible while deterring Russia’s most menacing behaviour.

The other half of Hill’s underlying message to Congress was that the country’s political leadership was in danger of destroying the very ideals that had drawn her and generations of immigrants to the United States in the first place. And it was even worse than that: politicians were taking an axe to their own country at Putin’s bidding.

Her opening statement was a blunt rebuttal of a conspiracy theory adopted by Trump’s supporters in Congress that it was Ukraine, not Russia, that had meddled in the 2016 US elections, in favour of the Democrats, rather than Trump.

Facebook Twitter Pinterest Fiona Hill testifies before the House intelligence committee. Photograph: Andrew Harnik/AP

Hill called it “a fictional narrative that has been perpetrated and propagated by the Russian security services themselves”.

The previous day, Putin, unable to contain his glee, had told an economic forum in the Russian capital: “Thank God, no one is accusing us of interfering in the US elections any more; now they’re accusing Ukraine.”

Hill appealed to her inquisitors: “I would ask that you please not promote politically driven falsehoods that so clearly advance Russian interests.”

Devin Nunes, the ranking Republican on the committee, bridled at her remarks – unsurprisingly, as his role throughout the proceedings has been to propagate the conspiracy theory that Hill was talking about. Nunes insisted that Republicans had produced their own report about Russian interference and it was quite possible that two foreign governments had meddled.

In her answers to the initial round of questions, Hill took that argument apart. The judgment that Russia had successfully intervened in the election was underpinned by the consensus of the US intelligence agencies, and was based on facts, many of them in the public domain. The Ukraine story was built on falsehoods, many of them propagated through social media by the Kremlin.

It is a distinction that has been in danger of being washed away. Hill was there to re-establish clear lines, and it was not clear how Trump and his camp would respond. Trump, normally quick to launch attacks on perceived threats, especially women, had restrained his Twitter thumbs for the whole morning.

Republicans on the committee, even Jim Jordan, the most aggressive among them, veered away from taking her on directly.

Hill walked out of the committee room as she had walked in, unflappable and serious, apart from a single smile reserved for the uniformed policeman at the door as she left the chamber.