He Calls the Shots for New York’s Governor. He Lives in Colorado.

With the Democratic nomination all but assured last spring, Gov. Kathy Hochul of New York and her campaign team began to plot a pre-emptive television ad to protect against Republican attacks already bubbling up around rising crime.

Ad makers cut a 30-second spot, highlighting Ms. Hochul’s plan to secure city streets and subway trains. She told her campaign manager she was eager to see it on air, and she previewed it for donors at a private Park Avenue screening.

But the ad never ran. After rounds of debate, one voice rose above the others. “Let’s focus on abortion,” Adam C. Sullivan wrote in a note to senior strategists reviewed by The New York Times. Crime could wait.

A year later, the decision has come to be seen by many in Ms. Hochul’s orbit as a damaging miscalculation that helped her Republican challenger come dangerously close to upsetting her, and contributed to Democrats losing the House majority. It is also a testament to the unseen influence of Mr. Sullivan, an obscure operative who has leveraged a close bond with Ms. Hochul to become perhaps the most powerful political force in New York who almost no one knows.

Mr. Sullivan, 42, has no formal job title or social media presence. He operates a small consulting firm from his home in a Colorado mining town, delivering strategy directives on issues like public safety far from the streets of New York City, where crime has unsettled some residents. And his generous compensation — estimated to be in the hundreds of thousands of dollars — is mostly hidden from campaign records.

Yet 18 months into Ms. Hochul’s tenure, Mr. Sullivan’s fingerprints can be found all over New York, according to more than two dozen people who have worked with him closely.

He helped Ms. Hochul build her administration, advising her on early key hires; shaped two multibillion-dollar state budgets; and ran a 2022 election campaign that was criticized by Democrats for its lack of energy. Most recently, he helped the governor navigate the failed effort to muscle Justice Hector D. LaSalle onto the state’s highest court.

Now, as the de facto head of Ms. Hochul’s political operation, Mr. Sullivan has been deputized to revive New York’s embattled state Democratic Party. And the outcome could have significant implications for Democrats’ chances to retake the House.

Even by the Zoom era’s standards, the breadth of Mr. Sullivan’s influence from afar is unusual, puzzling much of New York’s clubby political establishment and exasperating many on Ms. Hochul’s own team.

Most governors have a trusted, all-around enforcer who carefully guards their political standing. Ms. Hochul met hers in 2011, when Mr. Sullivan helped her win a far-fetched special House election no one else thought she could. But rarely do people in his position phone in from 1,700 miles away or command so few relationships with key stakeholders.

“Managing New York politics from Colorado is like managing the war in Ukraine from New York,” Charlie King, a veteran Democratic strategist, said. “You can be a very good tactician, but things on the ground move incredibly fast and you may just not be close enough to the action.”

Many of those who work directly for Ms. Hochul’s political team and administration have taken an even harsher view. The Times spoke to more than 15 people at all levels who said Mr. Sullivan is known as a divisive presence. They related anecdotes of him disparaging subordinates, especially younger women; marginalizing those who disagreed with him; telling younger workers that the governor did not know their names; and frequently shifting blame when things have gone wrong.

The aides and advisers insisted on anonymity for fear of retaliation. But they said Mr. Sullivan had contributed to Ms. Hochul’s diminished political standing while escaping public scrutiny.

In a written statement, Mr. Sullivan did not directly dispute those characterizations, but noted the intensity of the campaign. “I have always tried to treat everyone with respect and regret that there are people who feel I did not meet that bar,” he said.

Julie Wood, a spokeswoman for the governor, did not address the workplace concerns in her own statement about Mr. Sullivan, saying that the Ms. Hochul “values his ideas and guidance.”

“Ultimately what drives her decision-making is what’s best for New Yorkers,” Ms. Wood said.

There are also questions about how and by whom Mr. Sullivan, who is not a state employee, is being paid.

Since 2021, the governor’s campaign has paid roughly $50,000 directly to a limited liability company that Mr. Sullivan controls, “ACS Campaign Consulting.” But he earned far more through a secretive arrangement that rewarded him with a cut of the campaign’s ad spending, according to four people with direct knowledge of the matter. Assuming the arrangement was in line with industry standards, he would have netted at least $500,000 — a figure he did not dispute.

The Times could only identify one other current client of Mr. Sullivan’s, the Reform Alliance, a nonprofit founded by the rappers Meek Mill and Jay-Z and others to change probation and parole laws. Mr. Sullivan would not identify other clients, but he said that none had business before New York State. He added that he had “never been paid to lobby or influence the governor.”

The governor has leaned on other outsiders for help: The state paid nearly $2 million to Deloitte and Boston Consulting to help her with State of the State messages. Others with Ms. Hochul’s ear include Karen Persichilli Keogh, her top government aide; Jefrey Pollock, her longtime pollster; and Daniel French, who was until recently Syracuse University’s general counsel.

While those advisers are mostly known in political circles, even basic biographical information about Mr. Sullivan is difficult to find. Ms. Hochul has mentioned him prominently only once, from the stage after her victory in November. And he seems to be his consulting firm’s lone employee, working mostly out of his home in Leadville, Colo., where he is an avid skier, except for occasional trips to New York.

Of two dozen lawmakers, union leaders and campaign strategists contacted by The Times, only a few could correctly identify him.

“I’ve never met him, I’ve just heard bad things about him — sorry,” Liz Krueger, an influential Democratic state senator from Manhattan, said.

Mr. Sullivan’s proponents describe him as a talented tactician who steered Ms. Hochul through the aftershocks of Gov. Andrew M. Cuomo’s resignation and helped her win a full term in office, even if it was bumpy.

“Maybe he’s not the New York backslapper who knows everybody, but Adam has an unquestionable record of success,” Jess Fassler, Senator Kirsten Gillibrand’s longtime chief of staff, said.

Mr. Sullivan began his career as a political operative in 2000, and ran his first New York race in 2008, the same year he helped Ms. Gillibrand win re-election to the House.

He was fresh off a stint with the Democratic Congressional Campaign Committee in early 2011 when Ms. Hochul, then the Erie County clerk, decided to run in a special House election in western New York. She hired Mr. Sullivan as campaign manager because of his experience running special elections and his conviction, shared by few, that she could win. Despite long odds, she did.

It was a boon for Mr. Sullivan. He managed a Senate race in New Mexico in 2012 and was Senator Mary Landrieu’s campaign manager in her failed re-election bid in Louisiana in 2014, until he was abruptly fired just weeks before Election Day.

Ms. Landrieu said in an interview she had replaced Mr. Sullivan because she was losing and wanted a more familiar team. Afterward, Mr. Sullivan’s political work dried up, and Ms. Hochul appears to have been his only major political client since 2015.

Things began to shift in summer 2021, as it became clear that sexual harassment claims would force Mr. Cuomo from office. With only a small circle around her, Ms. Hochul leaned on Mr. Sullivan, whose wedding she attended in 2018, to help build an administration, including choosing Brian A. Benjamin as lieutenant governor. (Mr. Benjamin later resigned amid federal corruption charges.)

Mr. Sullivan played an even more active role in the campaign, involving himself in media strategy, Ms. Hochul’s day-to-day schedule and larger decisions like how to allocate millions of dollars on ad campaigns, including the one he intervened in last May.

In that case, the campaign produced and tested the ad, “Safe,” to highlight public safety changes approved in the state budget. Ms. Hochul and other advisers pushed to air it across New York. In the communications viewed by The Times, Ms. Hochul’s campaign manager, Brian Lenzmeier, wrote that she “believes strongly that we need to get a crime ad into the mix and not be solely focused on abortion.” (Mr. Lenzmeier declined to comment.)

But Mr. Sullivan often insisted that crime was a losing issue for Ms. Hochul. He believed the campaign’s resources would be better spent motivating Democrats to turn out on the issue of abortion rights, so he pushed to limit public safety messaging in areas like Long Island or to issues like gun laws. In the end, the campaign did not meaningfully challenge Republicans on crime statewide until October, after they had already whipped up a frenzy.

Ms. Hochul survived by just six percentage points in an overwhelmingly Democratic state, and some party leaders believe her approach on crime helped Republicans win congressional seats. Representative Nancy Pelosi, the former House speaker, told The Times’s Maureen Dowd that Ms. Hochul needed to deal with crime “early on, not 10 days before the election.”

Mr. Sullivan’s allies said he stood by the campaign’s commitment to prioritizing attacks on Ms. Hochul’s Republican opponent on abortion. Mr. Sullivan declined to comment on campaign strategy.

Since then, he has also resisted any quick course correction at the state Democratic Party. He and Ms. Hochul have stood by its chairman, Jay Jacobs, who has become a punching bag for Democrats, especially on the left.

Mr. Sullivan’s allies say he and Ms. Hochul want to strengthen the party, but they could only describe vague plans. In the meantime, national Democrats do not appear to be waiting, announcing their own $45 million New York political machine.

“Adam is the first person to pick up the phone and call me and be supportive,” Mr. Jacobs said in an interview. “I don’t think he has any agenda other than the governor being successful.”

Susan C. Beachy contributed research.