DAVIE, Fla. — Vice President Joseph R. Biden Jr. said on Thursday night that he was unsure whether he and his family had the “emotional energy” for a presidential bid, telling an audience at an Atlanta synagogue that “I can’t you look you straight in the eye and say now, ‘I know I can do it.’ ”

Mr. Biden, taking questions after delivering a foreign policy address, said that it “would not be appropriate” to mount a campaign unless he could devote himself fully to it. The vice president is still reeling from the death of his son Beau three months ago, and he said there was “no way to put a timetable” on the grieving process.

On a conference call last week, Mr. Biden made a similar reference to uncertainty about his family’s “emotional fuel” for a campaign. He said on Thursday that if he decided that he and his family could undertake the commitment, and that he could make a viable bid, “I would not hesitate to do it.” But, he added, “the honest-to-God answer is I just don’t know.”

His remarks represented his most expansive discussion of his deliberations since he began weighing a run more than a month ago. He has been looking more seriously at a campaign as Hillary Rodham Clinton, the Democratic front-runner, copes with falling poll numbers amid a growing controversy around her use of a private email server while she was secretary of state.

Aides say Mr. Biden may not decide until early October or perhaps later. The first Democratic presidential debate is scheduled for Oct. 13, and some states require that candidates qualify by early November to be placed on primary ballots.

The vice president spoke in Atlanta after making a two-day trip to South Florida — one of the most fertile grounds in the country for raising money for presidential campaigns — but he offered few clues about his thinking in his Florida appearances. He gave a speech at a community college, attended a fund-raiser for the Democratic Senatorial Campaign Committee and tried to persuade skeptical Jews about the merits of the deal to contain Iran’s nuclear program.

Instead, his trip became a measure of just how far the Obama administration will go to persuade one more lawmaker to vote in favor of the Iran deal, even after securing enough votes to ensure that it moves forward. Mr. Biden sat for nearly three hours around a horseshoe table here with 32 prominent Jews and talked. And talked. And talked.

The focus of his remarks, according to political analysts, was Representative Debbie Wasserman Schultz, a Florida Democrat who is also the chairwoman of the Democratic National Committee.

Traditionally, the head of the president’s party committee can be counted on to support and fight for every major White House priority, and there is no higher foreign policy priority for Mr. Obama than the Iran nuclear agreement.

But Ms. Wasserman Schultz has said she remains undecided. Her district is heavily Jewish, and many of her most prominent supporters are strongly against the deal. One protester outside her office recently screamed that “Wasserman Schultz should go to the ovens“ because, he suggested, she would support the deal.

Hundreds of people protested the deal outside the community center Thursday morning.

Before Mr. Biden spoke, Ms. Wasserman Schultz told the invitation-only gathering, “I am never afraid to stand alone, when necessary, to stand on principle.”

“This is a decision not only to be made based on your head,” she said after saying that she had closely studied every detail of the deal, “but one that will be made based on my Jewish heart.”

Ira M. Sheskin, an expert in Jewish American demography at the University of Miami, said that in polls, most Jews in the United States actually supported the nuclear deal, but those who were opposed were adamant about their opposition.

“The people who are for it are just barely for it, and the people who are against it are vehemently against it,” Professor Sheskin said. “Debbie’s dilemma is that this is one of those issues that no matter what she decides, people will be upset with her.”

Ms. Wasserman Schultz said that in several meetings with Jewish leaders across her district, most opposed the deal. She said she still needed to speak to nuclear experts and foreign diplomats as part of her research and promised to make a decision before Tuesday, when Congress comes back into session.

Political analysts said that Mr. Biden’s visit would give Ms. Wasserman Schultz some help with her constituents if she decided to support the deal.

Mr. Biden then told the gathering that he had spent his entire political life standing up for the state of Israel. But he also said he had decades of experience negotiating arms control agreements, and that he had little patience for those who argued that the United States should never negotiate with its adversaries.

Mr. Biden spoke about several details of the agreement and addressed head-on many of the arguments posed by the deal’s critics, including those in television ads.

There is “one thing I want to set straight because I’ve seen the ads,” Mr. Biden said. “That is the idea that we can’t inspect military facilities — it’s simply not true. Let me get this straight. Look at me. As one person once said, ‘Read my lips.’ Not true,” he said to laughter. “We can, with cause, inspect any place in Iran if we believe there is illegal activity taking place.”

Participants at the event spent almost two hours asking questions, a session that reporters were not allowed to observe. Baruch Levy, a dual citizen of Israel and the United States and a member of the national council of the American Israel Public Affairs Committee, known as Aipac, said he left the meeting still opposed to the Iran accord.

“But we were amazed and honored that he would explain over a period of nearly three hours all the details knowing that the nuclear deal is going to be approved,” Mr. Levy said. “However Ms. Wasserman Schultz votes, I will continue to respect her enormously.”