Donald J. Trump delivered a blistering attack on Wednesday against Hillary Clinton, calling her unreliable and more concerned with herself than with the American people as he sought to regain his footing after a tumultuous month that imperiled his candidacy.

In a 41-minute speech seeking to build his case against the presumptive Democratic presidential nominee by labeling her a “world-class liar,” Mr. Trump moved to soothe concerns among Republicans alarmed by gaping self-inflicted wounds after his racial attacks on a federal judge and his self-congratulatory boast after the terrorist shooting in Orlando, Fla. He said Mrs. Clinton would not create jobs, portraying her as a scandal-tarnished former secretary of state who “may be the most corrupt person ever to seek the presidency.”

“The choice in this election is a choice between taking our government back from the special interests, or surrendering our last scrap of independence to their total and complete control,” Mr. Trump said.

The professionalized presentation, with two teleprompters flanking the lectern in a third-floor ballroom of the Trump SoHo hotel in Manhattan, represented a stark contrast to how Mr. Trump has handled the last month of his campaign, and came two days after he fired his much-maligned campaign manager, Corey Lewandowski.