When George Helmy is sworn in next month as Robert Menendez’s temporary replacement in the Senate, he will be joining a chamber where Democrats hold a razor-thin majority, outnumbering Republicans by a single seat, 50 to 49.
Mr. Helmy was selected last week by Gov. Philip D. Murphy of New Jersey, a Democrat, to fill a seat held for three terms by Mr. Menendez, who, before being convicted of trading his political influence for bribes of cash, gold and a Mercedes, was widely viewed as one of the country’s most powerful Democrats.
Mr. Helmy, however, is new to the Democratic Party.
He registered as a Democrat in March, six days before the candidate he was supporting in the Democratic Senate primary, Tammy Murphy, New Jersey’s first lady, dropped out of the race, according to Board of Elections records in Morris County, N.J. Before then, he was registered as an independent — or “unaffiliated” — voter.
Mr. Helmy will serve in Washington only through November. He said that he will caucus with the Democratic Party after he is sworn in the week of Sept. 9, and will be a reliable vote for legislation supported by Senator Chuck Schumer of New York, the majority leader, and President Biden. His appointment will return the Democratic majority to 51 members, as it was before Mr. Menendez resigned on Tuesday. That includes four independents who caucus with the Democrats.
“I’ve worked my entire career to advance Democratic priorities,” Mr. Helmy said Friday in an email, “and that’s what I’ll continue to do during my short tenure as a U.S. Senator.”
In selecting Mr. Helmy, Mr. Murphy passed over Representative Andy Kim, who ran a bruising Senate race against the governor’s wife and went on to win the Democratic primary with 75 percent of the vote. Supporters of Mr. Kim, including Senator Cory Booker of New Jersey, had urged the governor to immediately appoint the three-term congressman to Mr. Menendez’s seat, giving him a slight seniority edge in the Senate and a possible head start toward preferred committee assignments.