It's almost as if Scott Walker knew he could get in trouble just by traveling to London. In the UK for a trade mission, the governor of Wisconsin and likely presidential candidate went to the Chatham House think tank to talk Wisconsin business on Wednesday — and ended up the headline of stories about, of all things, evolution.

Walker seemed to suspect something was coming. Answering a question about political polarization, he brought up the unpredictability of media coverage and referred specifically to the recent London visit of New Jersey Gov. Chris Christie, who ended up on the defensive over comments about vaccines.

"Look at my colleague, my friend," Walker said, referring to Christie. "When he came here a week or so ago, and I'm not going to get into his statement, but just saying that became the focus [of news coverage] … even though that probably wasn't the most substantive thing he was talking about here. And yet for whatever reason, that was the lead in many ways on the news."

Twelve minutes later, something similar happened to Walker, despite all his efforts to play it safe.

Walker was in the UK in his capacity as governor, to promote the sales of Wisconsin products. Yes, it's hard to view an overseas trip, especially by an American governor with presidential ambitions, as anything but a campaign event. But Walker steered clear of politics and didn't take any members of his presidential political team along with him.

As befits a representative of Wisconsin, Walker talked a lot about cheese. He wants the world to buy and enjoy vast quantities of Wisconsin cheese. His enthusiasm gave rise to far too many lame cheese jokes at venerable Chatham House.

Walker also said many deeply boring things about Wisconsin trade. Things like: "Thanks to God and the glaciers, we have the best industrial sand in the United States, and arguably in the world."

After Walker's speech, the Chatham House audience of journalists and businesspeople not surprisingly had questions that touched on U.S. foreign policy. Walker took particular care to avoid criticizing President Obama, adhering to the now-quaint idea that an American politician should not criticize his country's leaders while abroad.

For example, a reporter asked whether Britain should contribute more to the fight against the Islamic State. Any Republican running for president might well have answered that President Obama should contribute more to the fight against the Islamic State. Not Walker. "I defer to the president, even though I don't always believe in the same things that he does politically," Walker said.

Justin Webb, the BBC presenter moderating the session, remarked that in today's hyper-partisan world, Walker's response was "almost an old-fashioned way" of dealing with such issues.

"When you're in any country, not just the United Kingdom," Walker answered, "no matter what my opinions might be of this President of the United States right now, I just don't think it's wise to undermine the president of your own country."

And so it went. Walker was happy to talk about unions, health care, the University of Wisconsin budget, trade agreements, oil exports, and more. And then, 44 minutes into a 45 minute question-and-answer session, Webb turned to Walker and said: "We're out of time, governor. I know you have to be somewhere else. Can I finish with a question — it's almost a tradition now to ask visiting, particularly Republican, senior Republicans who come to London. And it's not about cheese, and it's not about foreign affairs. It's actually about evolution. Are you comfortable with the idea of evolution? Do you believe in it? Do you accept it?"

"For me, I'm going to punt on that one," Walker said. "That's a question a politician shouldn't be involved in one way or the other, so I'm going to leave that up to you."

Up until that moment, the story of the London trip might have been Walker's deference to Obama. Instead, it became, in the words of an Associated Press headline, "Wisconsin Gov. Walker Refuses to Answer Evolution Question."

Walker's political team back home scrambled to fix things, releasing a statement saying he believes "faith and science are compatible." But remarkably, for a man who has run for high office, Walker didn't have a ready-to-repeat answer on evolution. His staff didn't even know his views before drafting the statement.

But Walker learned a few lessons. First, there's no protection from out-of-the-blue questions. Second, Republicans, as Webb suggested, get special treatment when traveling abroad. And third, it doesn't matter if a candidate wants to talk about cheese and industrial sand, he's never the one setting the agenda.