There are a lot of advantages to having President Obama as your campaign cheerleader. He brings energy, wit and manifest rhetorical gifts. But, as Hillary Clinton learned on Tuesday, there is also a downside. He is an electrifying presence and accustomed to occupying center stage. And when he came to North Carolina for his first campaign event with the presumed Democratic presidential nominee, it seemed he could not help himself.

Scene-stealing pantomime

It began before he said a word. As Mrs. Clinton commended the man she hopes to succeed, the president held forth silently behind her, seated in a chair like an honoree at an awards dinner. He started playing to the crowd as she spoke. He mock-cried when she mentioned his daughter’s 18th birthday. He wiped his brow in dramatic fashion when Mrs. Clinton invoked their grueling 2008 race. The audience chuckled on cue.

“We’re fired up and ready to go,” Mrs. Clinton said as she wrapped her introduction, echoing a favored Obama refrain.