President Donald Trump is taking the country down the same path that led to U.S. entry into World War II, Sen. John McCain warned today, spelling it out for reporters who appeared not to get the message he delivered Monday night in Philadelphia.

On Monday, McCain blasted isolationism, declaring “unpatriotic” those calls to abandon the country’s role as international leader.

“To fear the world we organized and led for three-quarters of a century, to abandon the ideals we have advanced around the globe, to refuse the obligations of international leadership and our duty to remain the last best hope of earth, for the sake of some half-baked, spurious nationalism cooked up by people who would rather find scapegoats than solve problems, is as unpatriotic as an attachment to any other tired dogma of the past that Americans consigned to the ash heap of history,” McCain charged in accepting the Liberty Medal at the National Constitution Center in Philadelphia.

“We have done great good in the world. That leadership has had its costs, but we have become incomparably powerful and wealthy as we did. We have a moral obligation to continue in our just cause. And we would bring more than shame on ourselves if we don’t,” he warned.

“We will not thrive in a world where our leadership and ideals are absent. We wouldn’t deserve to.”

Trump responded Tuesday morning: “I hear it. People have to be careful because at some point I fight back. I’m being very nice. I’m being very, very nice. But at some point I fight back, and it won’t be pretty,” Trump boasted, in one of several interviews today with conservative radio hosts.

And media outlets asked McCain to respond.

“I’ve faced far greater challenges than this,” said the six-term senator, who served in the Navy more than two decades, was held prison for years by the North Vietnamese and recently was diagnosed with an aggressive form of brain cancer.

Later, when buttonholed by CNN, and asked if his previous night’s speech had been about Trump or Steve Bannon, McCain shot back, “I think what is clear is that I was talking about an environment here of non-productivity, of a reversion to the attitude of the ’30s, which was one of the major reasons why we fought World War II.”