When President Obama travels to North Carolina and Europe this week, he will press an argument that could define foreign policy in the last six months of his presidency: that Americans and Europeans must not forsake their open, interconnected societies for the nativism and nationalism preached by Donald J. Trump or Britain's Brexiteers.

Few presidents have put more faith than Mr. Obama in the power of words to persuade audiences to accept a complex idea, whether it is the morality of a just war or the imperfect nature of American society. Yet countering the anti-immigration and anti-free-trade slogans in this election year will require all of his oratorical skills.

Mr. Obama road-tested his pitch over the last two weeks in two friendly venues: Silicon Valley and Canada. This week, he will take the case to North Carolina, a swing state that has been hard hit by the forces of globalization, and to a NATO meeting in Poland, where the alliance members will grapple with the effects of Britain's vote to leave the European Union, known as Brexit.