"My biggest concern was my president," Booker said Monday on "The Tonight Show with Jay Leno."
"Barack, the president of the United States, was my friend before he was my president. I met him in 2005 and began a relationship with him and that's why I came out and was one of the first Democrats in the region to support his presidency," Booker said.
In May, during an interview on NBC's "Meet the Press," Booker condemned an Obama campaign ad that attacked presumptive GOP nominee Mitt Romney's tenure at private-equity firm Bain Capital.
“This kind of stuff is nauseating to me on both sides,” Booker said in the interview. The Newark mayor equated the Obama ad with attacks on Obama over for his former pastor, the Reverend Jeremiah Wright.
Booker almost immediately walked back his remarks, issuing a statement via Web video the same Sunday that emphasized his support for Obama and clarified his comments.
“I used the word 'nauseating' on 'Meet the Press' because that’s really how I feel when I see people in my city struggling with real issues,” said Booker in the video. “I get very upset when I see such a level of dialogue that calls us to our lowest common denominators and not the kind of things that can unify us as a nation and move us forward as a nation."
The Republican National Committee (RNC) seized on his remarks at the time, launching a petition drive urging voters to “stand with Cory" and painting a rift between the president and his Democratic ally.
The Newark mayor, a surrogate for Obama and popular personality in the Democratic Party, praised the president's handling of the situation on "The Tonight Show."
"During this time when other people might have been saying things about me, he was incredibly gracious in the things he said about me. I've seen him since. We continue to be friends. He was incredibly kind," Booker said.
Booker also told Leno that the president was the "first person" to reach out to him after the Sunday show debacle.
"He was the first person to step forward and say, 'Hey, you're my friend. We all say things that don't come out as we mean them and I'm still with you,' and I'm still with him," Booker said.
Obama publicly defended his campaign's attacks on Romney's role at Bain Capital following Booker's initial remarks.
“The reason this is relevant to the campaign is my opponent, Gov. Romney, his main calling card for why he should be president is his business experience,” said Obama during a speech in Chicago last month.
During "The Tonight Show" interview, Booker also deftly avoided questions about possible ambitions for the Garden State governorship, pivoting and asking Leno "are you going to run for it?"
Although there has been speculation that Booker could run for Gov. Chris Christie's seat next year, the Republican governor and Democratic mayor have crossed party lines for the sake of their state, even releasing a spoof video in May that mocked their perceived rivalry.