What is fair is to observe that the Republicans’ claim that they are the great job creators is a fiction.

Prof. Robert S. McElvaine of Millsaps College examined employment data for the 64 years from the beginning of Harry Truman’s presidency to the end of George W. Bush’s. He found that an average of two million jobs were created per year when a Democrat was president, compared with one million annually when a Republican was president.

More pointedly, and unfortunately for Romney, business executives have only a mediocre record when transferring their skills to government. In the last great economic mess, this country was led by a Republican who had been stunningly successful in business: Herbert Hoover. Hmm. More recently, President George W. Bush staffed his cabinet with C.E.O.’s who had been stellar in the private sector — and that didn’t work out so well, either.

Obama’s point about our shared undertaking was made last year, more eloquently, by Elizabeth Warren, the Massachusetts Democrat running for Senate:

“There is nobody in this country who got rich on his own — nobody!” she said. “You built a factory out there? Good for you. But I want to be clear: You moved your goods to market on the roads the rest of us paid for; you hired workers the rest of us paid to educate; you all were safe in your factory because of police forces and fire forces that the rest of us paid for. ...

“You built a factory, and it turned into something terrific or a great idea? God bless. Keep a big hunk of it. But part of the underlying social contract is, you take a hunk of that and pay forward for the next kid who comes along.”

In short, taxes don’t just smother. They can also fuel growth — when they’re invested in highways or the Internet, in colleges or early childhood education. They can create opportunities, as they did for Sher Valenzuela.