Who Is Bill Stepien? A Data-Obsessed Campaign Manager for Trump’s 2020 Campaign

In firing Mr. Stepien, Mr. Christie cited a “tone and behavior and attitude of callous indifference” in Mr. Stepien’s emails that “made me lose my confidence in Bill’s judgment.”

But the two have since reconciled.

“Even during that period of time, when then-candidate Trump came to me and asked me in ’16 about whether or not he should hire Bill, I told him he absolutely should,” said Mr. Christie, who said he now talked with Mr. Stepien multiple times a week. “There was not any falling out in terms of my trust in Bill’s skills during that period of time.”

Mr. Stepien, 42, got his start in politics in 1997, when he was still a student at Rutgers, volunteering for the campaign of State Senator Anthony R. Bucco of New Jersey. Mr. Stepien would work overnight in the headquarters, coming after hockey practice to send out mailers to absentee voters, reminding them to return their ballots on time.

From there, Mr. Stepien slowly climbed the ranks of New Jersey politics. He served as the driver for a Senate run by Bob Franks in 2000, as a lower-level staff member for Mr. Franks’s race for governor in 2001, and as the campaign manager for Bill Baroni’s State Assembly race in 2003, in which Mr. Baroni beat a Democratic incumbent in a traditionally Democratic district.

The Baroni victory put Mr. Stepien on the map in New Jersey. Mike DuHaime, a longtime New Jersey political operative, brought him into his consulting firm, a job that led to positions at the Republican National Committee and on the 2008 presidential campaigns of Rudolph W. Giuliani and Senator John McCain.

But his political breakout came with Mr. Christie in 2009, when Mr. Stepien managed his first campaign for governor. Though their opponent, Jon Corzine, was a vulnerable incumbent, Mr. Christie was also facing an independent candidate, Chris Daggett, whom internal campaign polls had at nearly 20 percent, keeping Mr. Christie stuck at 40 percent.

Mr. Stepien, along with Mr. DuHaime and Mr. Christie, hired TargetPoint, a Republican data firm, to ask Mr. Daggett’s supporters whom their second choice was.