There’s this thing that happens when you talk to the president. You kind of stop paying attention. I mean, you’re paying attention, of course, but you’re not really listening, if you know what I mean. You’re thinking about what you should ask next, about how much time you have left — which is never enough — and a thousand other things.

Which is why — early in our interview today — he caught me up short.

I’d asked him about China, about how sure he is that once we and the other Trans-Pacific Partnership countries write the trade rules for the region, that the Chinese will follow. Because it’s a pretty big deal that the second-biggest economy in the world isn’t in the biggest trade deal the U.S. has had in a generation.

He started talking, and I started thinking about where to take the interview next, and then he said, “Well, they’ve already started putting out feelers about the possibilities of them participating at some point.”

That would be a big (trade) deal.

Economists can, and do, argue about free trade all the time. But it’s pretty much accepted wisdom that in the aggregate — and that’s the key word here, aggregate — free trade is a net positive.

The catch, of course, is that with winners come not-winners, and so I asked the president about that.

“The question is, ‘Are there a lot more winners than losers?’ And the answer in this case is, ‘Yes.’ But that doesn’t mean that there is not going to be some impact on some sectors of the economy, by definition,” he said.

A lot of the pushback against the TPP is coming from the president’s side of the aisle: Democrats who remember the North American Free Trade Agreement and what it meant to a lot of their constituents — lower wages and lost jobs. Which the president gets. Kind of.

“The argument that I make to my friends, whose values I share, is that you can’t fight the last war,” he said.

This time, he says, will be different, with tougher regulations and higher standards covering workers who make up almost 40 percent of the entire global economy.

“If we’ve got potentially hundreds of millions of workers who are now subject to international labor standards that weren’t there before, and now when we’re working with them, even if they’re not enforcing those standards 100 percent, we’ve got enough leverage to start raising those standards,” he said.

And really, he said, it’s not like we’ve got a choice.

“We are completely woven into the global economy. We’re the hub to many, to a large extent of the global economy,” he said. “The question is, ‘How do we construct a set of rules and how do we make sure we’re adapting and using the incredible advantages we have to the best of our ability?’ ”

To read the full interview with President Obama, click the “Transcript” tab at the top of the story.