CLEVELAND — It was just after 10:30 p.m. Tuesday, a coveted time slot at any political convention. But at the Quicken Loans Arena here, there were rows and rows of empty seats as Kimberlin Brown, a soap opera actress and California avocado farmer, struggled to talk over the chatter of delegates heading for the exits. The session was supposed to last until 11 p.m.; the gavel fell at 10:58.

Donald J. Trump came here promising a nominating convention bursting with glitz, energy, celebrity and the highest of show business production values. Instead, at least for the first two nights, Mr. Trump struggled to stage the biggest show of his political career: his own convention.

The party gathering, after an unusually contentious primary season, has been marked by a noticeable absence of energy and swaths of empty seats. The audience, whose attention often seems elsewhere, responded to a historic moment — when Mr. Trump’s son Donald Jr. cast the votes that made his father the Republican presidential nominee — with modest applause. Chants of “Trump-Trump-Trump” rose in one section of the floor, only to fade away.

The crowd seemed to come alive only when the subject was not Mr. Trump but Hillary Clinton, the likely Democratic nominee. “Lock her up, lock her up, lock her up!” the crowd chanted lustily as Chris Christie, the New Jersey governor whom Mr. Trump defeated for the nomination, offered an indictment of Mrs. Clinton.