In June, Mr. Rose attended a demonstration in Staten Island to protest the death of George Floyd. His participation became a focal point of Ms. Malliotakis’s campaign, enabling her to accuse Mr. Rose of being a supporter of efforts to defund the police.
“She exploited Rose’s moderacy, and made much of the fact that he participated in a B.L.M. rally, and that played really well with the communities in the South Shore,” said Richard Flanagan, a professor of political science at the College of Staten Island.
Mr. Rose had characterized his participation in the protest as a gesture of unity.
“For a brief moment, we didn’t see each other as Democrats or Republicans, but as Americans in pain and searching for a way to heal,” he said in an election night speech. “It may feel like a long time ago.”
Being viewed as anti-police and, for that matter, anti-Trump, probably hurt Mr. Rose in the conservative district, even though it has slightly more registered Democratic voters than Republican. For much of the last 75 years, a Democrat has held the seat; in the past decade, though, two Republicans, Michael Grimm and Dan Donovan, won the office.
For a first-time House candidate, Ms. Malliotakis, 39, had ample name recognition: In addition to her work in the State Legislature, she also ran for New York City mayor in 2017.
“This city has seen a significant shift to the left that’s made a lot of people uncomfortable in our community,” she said in an interview the day after Election Day. “I will be a voice that will provide a different perspective, and that’s where you get good policy — when you have a debate and hopefully end up somewhere in the middle.”
She spent her campaign tying Mr. Rose to his more progressive peers, including House Speaker Nancy Pelosi, Representative Alexandria Ocasio-Cortez and Mayor de Blasio.