Wisconsin Governor Scott Walker talks during an interview with the Associated Press in New Orleans, Monday, May 18, 2015. (AP Photo/Gerald Herbert)

The Milwaukee Journal Sentinel reported this week:

Scott Walker said Wednesday that he will stop talking about private meetings with world leaders after British Prime Minister David Cameron disputed that he had disparaged President Barack Obama’s leadership in private comments to the Wisconsin governor.

“I’m just not going to comment on individual meetings I had with leaders like that, be it there or anywhere else,” the White House hopeful told reporters when asked about Cameron’s response.

Walker on Friday told Republican donors at a Utah gathering that Cameron and other leaders were concerned about Obama’s “lead-from-behind mentality.”

Cameron’s office responded that the prime minister never expressed concerns about Obama in his February meeting with the governor.

The report quotes Walker as saying, “What I learned best from that is I should leave discussions like that that aren’t done in front of the media to be treated privately, whether it was there or anywhere else.”

On the one hand, a mini-kerfuffle this early in the race is unlikely to have any lasting effect. On the other hand, coming on the heels of Jeb Bush’s near-flawless overseas trip and Sen. Marco Rubio’s (R-Fla.) adept handling of all sorts of foreign policy questions, it should remind Walker and his supporters that he still has much to learn.

In particular, Rubio — the other “new generation” Republican reformer with appeal to working and middle class voters — poses a real challenge to Walker. Dorothy Rabinowitz writes:

Candidate Rubio has, and it is no small advantage, a gift for language found frequently in people who have been voracious readers from childhood on. Like many children with his history, he also imbibed the sense of American exceptionalism at an early age and it has not gone away nor is it likely to do so.

There is no love of country quite as deep or conscious as that of the first-generation American. Mr. Rubio is the child of immigrants, Cubans in this case, who tutored him, as other immigrant parents have done with their children, in the unparalleled blessings of America. . . .

In the course of his campaign rollout two months earlier than Mrs. Clinton’s, Mr. Rubio too addressed the dangers of leadership and ideas based on the values of yesterday. Only in his view those dangers were the obstruction of economic progress, the stifling of America’s ability to compete—and not least the failure to remember the importance of U.S. leadership in the world.

“And so they appease our enemies, they betray our allies, they weaken our military,” he says of the current administration. A dramatically different set of charges against yesterday’s thinking—and one with which virtually all Republican candidates would agree—than the compendium of victims suffering under the heels of Republicans and millionaires and billionaires that Mrs. Clinton cited on Roosevelt Island.

In other words, it may be that the policy outcome Rubio and Walker reach is quite similar, but Walker will find it hard to match Rubio’s verbal dexterity and comfort level on national security — at least for a while. Walker navigated some bumpy moments early in the year before he began his foreign policy studies and started traveling. For a time he seemed to have found his footing and was effective in interviews. But the bar rises as the campaign goes on, especially in side-by-side comparison with other candidates in debates and the like. As other candidates show their ability to navigate foreign policy issues Walker will have a smaller margin for error. And soon when he travels abroad, the expectation will be that he speaks and/or takes questions from the press.

The lesson for Walker is therefore two-fold: Don’t characterize publicly what foreign leaders say to you privately, and, more importantly, the goal posts will keep moving throughout the race, forcing each candidate to improve. For someone who has not spent his career delving into foreign policy and has no military experience, that means the learning process must continue throughout the primary and into the general election. It’s not enough as it was a couple of months ago to avoid big missteps or to just list Hillary Clinton’s errors. Candidates will need to instill confidence and demonstrate mastery of the ins and outs of international affairs. It is a tall order, but then no one ever said it was easy to become a credible commander in chief.