If ever there was a moment for Donald J. Trump to share the spotlight, his formal announcement of his running mate on Saturday was it.



Instead, his introduction of Gov. Mike Pence of Indiana was a remarkable reminder that ultimately, the Trump campaign is about one person.

He called Mr. Pence his “partner,” but before the governor took the stage, Mr. Trump stood there alone and talked for 28 minutes, delivering a long and improvised riff that emulated his rallies instead of a traditional vice-presidential debut.

Looking away from his notes, he talked about Hillary Clinton, terrorism, his primary victories, his crushing of a “Stop Trump” movement. Donald Trump, Mr. Trump said, understands infrastructure and how to build a border wall. He even got in a plug for his new hotel in Washington.