He waited all of 45 seconds to make clear he came not just ready for a fight but ready to pick one.

President Obama, who concluded that he was “too polite” in his first debate with Mitt Romney, made sure no one would say that after their second. He interrupted, he scolded, he filibustered, he shook his head.

He tried to talk right over Mr. Romney, who tried to talk over him back. The president who waited patiently for his turn last time around forced his way into Mr. Romney’s time this time. At one point, he squared off with Mr. Romney face to face, almost chest to chest, in the middle of the stage, as if they were roosters in a ring.

“What Governor Romney said just isn’t true.”

“Not true, Governor Romney, not true.”

“What you’re saying is just not true.”