As he spoke, it became clear that his remarks were less an introduction and more a homily, with more than a little biography thrown in. He was at times quiet and reflective, and at other times bellowing at the top of his lungs, leaving the crowd cheering, applauding and shouting in agreement.
"I don’t know about you, but I think we just heard a great sermon," Clinton said when some 15 minutes had passed and she was handed the microphone.
Booker's ascent and natural political gifts have made him one of the most promising young figures in the party. He has campaigned for Clinton before in states like South Carolina, New Hampshire, and Tennessee as a surrogate and ambassador -- including to the African American community. But their first appearances campaigning together in the 2016 election came on Sunday.
His appearance in Iowa eight days before the caucuses made him one of a handful of political and progressive figures brought out on the campaign trail to ratchet up the enthusiasm that Clinton's campaign hopes will help drive her supporters to the polls.
On display in the cafeteria of Vernon Middle School was Booker's ability to deliver a sweeping and rousing speech.
He reminded the crowd of more than 600 that though he was from New Jersey, his roots were here in Iowa.
"This is the land where my grandmother was born and raised — Des Moines, Iowa," Booker said. "My grandmother from Iowa, she is dancing in heaven at the prospect that the next president of the United States is going to be Hillary Rodham Clinton."
He spoke of his parents' struggle to buy a house in an all-white New Jersey neighborhood, where homeowners defied the law and refused to sell to a black couple. His father grew up "po"-- too poor to afford the last two letters. He spoke of his father's "tall tales" and his mother's attention to detail.
"Do not forget from whence you’ve come," Booker exhorted them. "Do not forget the history that made it possible for you to be here."
"My family is no different from yours. We may be different from the geography that we come from. Some of you all may pray differently than I do, some of you all may be from a different ethnicity, but we all have the same story," Booker said.
He cautioned against the giving into the "cynicism about our nation," which he called a "refuge of cowards."
"You all have po-wer! Think about it," Booker said.
"The most common way people give up their power is not realizing they have it in the first place," he added, quoting author Alice Walker.
And so he urged Iowans to use their power to elect Clinton, who he said would be "the most qualified person since George Washington" to serve as president.
"I’m telling you right now, that when Iowa speaks in a chorus of conviction...we will ensure and put a great American on the trajectory to the White House," Booker said.
Earlier in the morning, the two visited the predominantly African American congregation at Mt. Zion Missionary Baptist Church in Cedar Rapids for their Sunday service.
After Booker delivered the sermon on behalf of the church's absent pastor, it was Clinton's turn at the microphone and she praised Booker effusively.
"I think you all got more than a little taste about why this young man still, is still so special to so many," Clinton said. "He has given of himself in very personal ways, living with people who felt left out, left behind, working to improve their lives, to create economic and educational opportunity.
"And it gives me such a sense of gratification that he is here, supporting me in this very important election, because there is nobody I'd rather have by my side," she added.