(CNN) On Monday night in Philadelphia, John McCain offered a total and complete rejection of the world view offered by the leader of his party.
Here's the key paragraph:
"To fear the world we have 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."
"Half-baked." "Spurious nationalism." "Tired dogma."
Those would be harsh words coming from any politician about the president of the United States. They are remarkable when you consider that McCain and President Trump are, ostensibly, part of the same Republican party.
What McCain's speech shows -- again -- is just how far Trumpism is from the traditional Republican party on virtually every issue. And how much Trumpism represents a break from the ways in which all post-World War II presidents -- Republican and Democratic -- have envisioned the role the U.S. can and should play in the world.
(Perhaps the most moving part of McCain's speech was when he recounted attending an event in which George H.W. Bush was commemorating soldiers lost on Dec. 7, 1941; "May God bless them, and may God bless America, the most wondrous land on earth," McCain recounted Bush saying, with emotion heavy in his voice.)
That McCain is giving this speech isn't terribly surprising. He has always been someone who fancies himself as willing and able to critique his own party. And, his diagnosis earlier this year with an aggressive form of brain cancer has made him even more outspoken about the problems he sees in the party (and the country).
But, simply because McCain is someone who has been critical of Trump in the past doesn't make his speech last night any less important.
Remember what McCain has given to the country. Naval service. Six years as a prisoner of war. More than three decades in public office. Two presidential bids. This is someone who understands at a gut level what this country means -- and what it should mean -- around the world.
"What a privilege it is to serve this big, boisterous, brawling, intemperate, striving, daring, beautiful, bountiful, brave, magnificent country," McCain said on Monday night. "With all our flaws, all our mistakes, with all the frailties of human nature as much on display as our virtues, with all the rancor and anger of our politics, we are blessed."
That view of America -- who we are and who we should be -- is at direct odds with Trump's vision.
"Our convention occurs at a moment of crisis for our nation," Trump said in his speech accepting the Republican nomination in 2016. "The attacks on our police, and the terrorism in our cities, threaten our very way of life. Any politician who does not grasp this danger is not fit to lead our country."
On foreign policy, Trump offered a similarly grim assessment in that convention speech. "The most important difference between our plan and that of our opponents, is that our plan will put America First. Americanism, not globalism, will be our credo," he said. "As long as we are led by politicians who will not put America First, then we can be assured that other nations will not treat America with respect."
In office, Trump has made good on that rhetoric. He has decertified the Iran nuclear deal. He has pulled the US out of the Paris climate accords. At global summits, he has been adamant that the US will no longer write checks to fund the rest of the world.
McCain, in his speech Monday night, was not just rejecting Trump's dark vision of America and the world but he was seeking to point out how at odds that vision is from how all of the men who came before Trump in the office -- at least since the 20th century -- saw their job and the country.
These lines, in particular, speak to that divide -- and the dangers, in McCain's mind -- of pursuing Trumpism to its logical end. Said McCain:
"We live in a land made of ideals, not blood and soil. We are the custodians of those ideals at home, and their champion abroad. 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. We will not thrive in a world where our leadership and ideals are absent. We wouldn't deserve to."
Will other prominent Republicans speak out in support of McCain? Almost certainly not. To date, the only consistent voices of criticism against the rise of Trumpism within the GOP have been McCain and Sens. Bob Corker of Tennessee, Ben Sasse of Nebraska and Jeff Flake of Arizona. (Of McCain's speech, Corker said Tuesday: "Well the pieces that I saw, I loved, and I gave him a big hug on the floor.")
Corker is retiring and Flake is in deep trouble for reelection. Sasse appears, at least at the moment, to be the one whose willingness to stand against Trumpism hasn't negatively affected his political future.
Regardless of whether other Republicans rise to support him, what McCain is trying to say is of critical import: Trumpism is neither conservatism nor Republicanism. The question is whether that will continue to hold true if no other voices rise to speak out against Trumpism.