With her strong handshake and assertive manner, it’s hard to imagine Elise Stefanik did not always possess the determination and self-belief it took to become America’s youngest woman ever elected to Congress.

But the 30-year-old New York Republican — who made history when she was sworn in Jan. 5 — was once the target of “mean girls” who undermined her confidence.

“I was singled out by other girls for participating in classroom discussions and physically bullied,” says Stefanik, recalling a fourth-grade experience when she was attacked for being “too studious.”

The final straw was a gym-class bully violently yanking a hair clip out of her head — and, when they complained to the administration of the Catholic school, Stefanik’s concerned parents being told that nothing could be done.

“That’s when they took things into their own hands and took me out in the middle of the year to go to a different school,” says the lawmaker, who landed a partial scholarship to the prestigious Albany Academy for Girls, where she went on to excel academically.

Two years later, she was running for secretary of the school council — and her platform included a new snack machine.

Today, from her position representing the vast 21st District in upstate New York, it would be easy for the rookie politician to feel as if she had the last laugh on the bullies — but she won’t have any of it.

“I do not look back at all and ever say: ‘Look at me now!’ ” she says firmly, with a smile that says she’s not to be messed with. “I’m just not that kind of person.”

She tells the story matter-of-factly, sitting in her compact Washington, DC, office in what feels like the attic of the representatives’ administration building on Capitol Hill. The suite of two rooms — which Stefanik was allocated by a lottery ranking the 435-strong Congress on seniority — is traditionally decorated. Formal pictures from district meet-and-greets and photographs of her family sit in frames on the table and desks.

She is particularly close to her father, Ken, who owns their family business, Premium Plywood Products, in Altamont, NY, where her mom, Melanie, and 25-year-old brother, Matt, also work.

As for Stefanik herself, she isn’t easily defined. The fresh-faced brunette got a BA with honors in government from Harvard in 2006, and she walks through the halls of the Capitol with her head held high in feminine frocks and 2-inch nude heels. But when she’s off-duty, you’ll find Stefanik behind the wheel of her Ford F-150 truck or with a Remington 870 shotgun slung over her shoulder to go skeet shooting, her hair pulled into a ponytail.

Three months into her first term, Stefanik is finding the balance.

The challenges are certainly harder when you’re a woman, because you’re under more scrutiny about your appearance than male colleagues. - Congresswoman Stefanik

“The challenges are certainly harder when you’re a woman, because you’re under more scrutiny about your appearance than male colleagues,” she says. “I usually try to wear stuff that is versatile, pretty classic.”

Her current go-to designer is the Manhattan label MM.LaFleur, founded by her pal Sarah LaFleur. But her style secret is finding deals on discount sites like Rue La La and Gilt.

In the early days of her term, there were frustrating mix-ups when she was either mistaken for a spouse or an assistant — a couple of cops ordered her off the members-only Capitol steps, and she got withering looks for riding on the members’ tram car, which runs, quite literally, under the corridors of power.

Stefanik has already learned to be fiercely protective of details of her personal life. She has a boyfriend of 3½ years but refuses to talk about him publicly.

And it’s no wonder she’s guarded. As a young, unmarried woman with no children, Stefanik has raised eyebrows among older critics, who’ve questioned what she brings to the table.

Her 2014 campaign, endorsed by The Post, survived a series of smear tactics.

In a mischief-making letter to a Watertown newspaper, an associate of her opponent, Democrat Aaron Woolf, asked: “Does Elise Stefanik have a private relationship with anyone?” In other words: Any juicy gossip on this woman?

Responds Stefanik: “I had previously talked on the campaign trail about having a serious boyfriend and that he was fully supportive of my race, but I was running as my own person and happy to answer whatever questions anyone wanted.”

The letter, as she puts it, “backfired.”

Another target of Woolf’s was Stefanik’s résumé. During one debate, he accused her of not knowing the definition of “real work” — “It’s a lot more than just sitting at a desk,” he sniffed.

The voters didn’t take the bait. Stefanik cruised to victory, defeating Woolf last November with 53.4 percent of the vote.

The former Bush administration West Wing staffer, whose most recent job was a mostly managerial role at her family’s company, insists her experience watching her parents “risk everything” to launch their own business has given her unique insight.

Her eyes light up when she talks about policy in her beloved home state. Gesticulating with her hands as she makes each point, her tone becomes serious as she mentions the faltering economy in the northernmost reaches of New York and the migration of young people south.

“One of my key issues is economic empowerment,” says Stefanik, clearly passionate about the day-to-day problems facing her remote district, which begins at the eastern shores of Lake Ontario, encompasses the Adirondack Mountains and stretches toward Canada in the north and Vermont in the east. Her folks have had a year-round second home in Willsboro, on the shores of picturesque Lake Champlain, since she was 3, where she now resides when she is upstate. Meanwhile, she owns a property in DC.

“It’s one of the most beautiful areas of the country, especially in summer,” says Stefanik, who clocked more than 100,000 miles in her trusty truck while drumming up votes in 2013 and 2014. “But it’s tough in winter.”

Stefanik splits her time between DC and upstate, taking every opportunity she can to head home. Some must-stop spots when she’s back include Whiteface Mountain near Lake Placid for skiing and the historic Revolutionary War outpost Fort Ticonderoga.

When she’s in DC, there’s less time for fun. She works 14-hour days on committees and on the floor of the House.

When she does have a moment free, her favorite hobbies include theater, playing on the congressional softball team, watching TV shows like “Veep” and reading contemporary fiction such as the thriller “Sharp Objects” by “Gone Girl” author Gillian Flynn.

When it comes to political ambitions, Stefanik doesn’t care to look much to the future, insisting she is concentrating on the job at hand and trying to be a positive role model for women.

She fondly recalls an event during her campaign run when a pair of upstate parents brought their elementary-school-age daughters to hear her speak.

“This was a nonpolitical family who’d never come to a rally,” says Stefanik. “But they wanted to show their daughters . . . what they can achieve, too.

“That was really humbling.”

Welcome to my New York!

Rep. Stefanik shares her eight favorite upstate spots:

Fort Ticonderoga (Ticonderoga)

“Growing up, my parents took my brother, Matt, and me to see Revolutionary War re-enactments at this historic fort.”

Gore Mountain (North Creek)

“I’ve been a skier since I was 2 or 3, skiing with my dad in northern New York and Vermont.”

Essex Inn (Essex)

“This light-yellow historic inn has always been one of my favorite buildings in the district. I love visiting the restaurant for a quiet night with exceptional food.”

Adirondack Coast Wine Trail (throughout Clinton County)

“My favorite is Vesco Ridge Vineyards [in West Chazy] — beautiful tasting room and outdoor space, excellent wine and gracious owners.”

Cascade Mountain (Essex County)

“We have 46 high peaks in the Adirondacks, which are the mountains over 4,000 feet. You are a ‘46er’ if you hike all 46. This is a goal of mine over the next 10 years before I turn 40.”

Stewart’s Shops

“Part grocery store, part corner store, part convenience store, part gas station, these are throughout upstate New York. Best ice cream and best milk! A daily stop for many NY-21 constituents.”

View arts center (Old Forge)

“I saw an amazing watercolors exhibit here in 2014 and am constantly blown away by the caliber of the exhibitions.”

Pearl Street Pub, aka the Mayor’s Bar (Watertown)

“The proud owner is also Watertown’s mayor. Jeff Graham is a die-hard politico and radio host with one of the best political blogs in New York state. Stop by there for a drink — you’re bound to run into the mayor! Tell him Elise sent you.”