As a first-term Republican congresswoman from upstate New York, Elise Stefanik was so reluctant to endorse Donald Trump’s bid for president that she refused to say his name aloud, instead referring to him as “my party’s nominee”.

Four years later, Stefanik had become one of the president’s fiercest defenders. In a coveted speaking spot at the 2020 Republican National Convention, she offered Trump her full-throated endorsement and described the Democrats’ impeachment probe as a “baseless and illegal . . . sham”.

Today, Stefanik, 36, is on the cusp of Republican party leadership. She is widely expected to be elected this week as House GOP conference chair, which would make her the most senior Republican woman on Capitol Hill. Trump last week endorsed her for the role, calling her a “tough and smart communicator”. She also has the public backing of Kevin McCarthy and Steve Scalise, the number one and number two House Republicans, respectively.

Stefanik is set to replace Liz Cheney, the Wyoming Republican and daughter of former vice-president Dick Cheney, who fell out with her party over her vote to impeach Trump earlier this year for his role in the January 6 attack on the US Capitol that left five people dead.

“Elise coming in is a perfect symbol for the Trump era,” said Brendan Buck, a former senior aide to Paul Ryan, who was Speaker of the House from 2015 to 2019. Stefanik worked on Ryan’s debate prep team when he was Mitt Romney’s running mate in the 2012 presidential election.

“By every measure, she is actually less conservative than Liz Cheney, but on the measures that matter — support for the president, willingness to fight the culture war, willingness to fight the media — she checks those boxes,” he added.

Cheney is a staunch economic and geopolitical conservative. But she has repeatedly called out colleagues for encouraging Trump’s false claims that the 2020 election was rigged against him.

Stefanik, meanwhile, last week appeared on Steve Bannon’s podcast and said she was “fully” supportive of Republican efforts to overturn the election results in Arizona, where Joe Biden beat Trump. She was one of 147 Republican lawmakers who voted against the certification of Biden’s Electoral College win, even after a violent mob of Trump supporters stormed the Capitol.

For many in Washington, that vote solidified Stefanik’s bona fides as a Trump loyalist — and underscored the dramatic change in style and substance for the Harvard University graduate. Stefanik had long been seen as a rising star from the moderate wing of the Republican party, with a resume that included stints working for former president George W Bush and ex-Minnesota governor Tim Pawlenty.

Stefanik was born and raised in Albany, New York, by parents who owned a plywood distributor. She demonstrated an interest in politics from an early age: a 1998 local newspaper article documented how then 14-year-old high school student Stefanik skipped class to attend a book signing for a Republican lawmaker.

She went on to Harvard, where she was active in student journalism and politics and earned a degree in government. As an undergraduate, she co-authored an opinion piece with Jeanne Shaheen, the former Democratic governor of New Hampshire who is now a US senator.

In 2014, she ran for office as a Republican and won her race for the US House of Representatives at the age of 30, making her the youngest woman ever elected to Congress.

In the 2016 cycle, Stefanik first endorsed John Kasich, the former Ohio governor, before grudgingly backing Trump as the Republican party nominee. Shortly after his election, she became co-chair of the Tuesday Group, a caucus of moderate Republican lawmakers committed to working with Democrats.

But less than three years later, she had tacked sharply to the right, joining Trump’s defence team in his first impeachment and becoming one of his loudest supporters. As a candidate in 2020, Stefanik adopted many of the president’s rhetorical flourishes, including giving her Democratic opponent, Tedra Cobb, the nickname “Taxin’ Tedra”.

Stefanik’s critics and allies alike say her political transformation reflects the changing views of voters in her congressional district.

“What [Stefanik] saw and realised is that the district was no longer a place that wanted a squishy, moderate Republican,” said Buck. “It wanted a fighter. It wanted what Donald Trump was selling, and so she reinvented herself.”

Stefanik represents New York’s 21st congressional district, which spans a significant portion of upstate New York. The largely rural, white working class district voted for Barack Obama in 2008 and 2012, before flipping to become solidly Republican in the 2016 presidential election. Trump beat Hillary Clinton and Joe Biden by 14 and 11 points there, respectively.

“People here, like they were nationally, were very willing to turn to Donald Trump’s message of reinventing . . . this America that existed, because things up here 60 years ago were better, objectively, than they are now,” said Alexander Cohen, a political-science professor at Clarkson University in Potsdam, New York, who said Stefanik now has a “stranglehold” on the seat.

Stefanik is one of the top Republican fundraisers on Capitol Hill, raking in $13.3m in the 2020 campaign cycle alone, according to OpenSecrets. Her leadership fundraising vehicle, E-PAC, funnelled $435,000 to other Republican women, helping the party double its number of female representatives in the House between 2018 and 2020.

The record puts her in good stead with fellow Republican lawmakers who will be looking to take back control of both the House and the Senate from Democrats in next year’s midterm elections.

But it will do little to offset attacks from Stefanik’s critics, who accuse her of flip-flopping when it comes to both personality and policy.

Cohen said he did not know if Stefanik’s political evolution reflected “naked ambition” or “real, ideological belief”.

But he added: “Of course it is hard to tell the difference between those two in politicians.”