In an op-ed on Friday, Sen. John McCain (R-Ariz.) called on Congress to focus on its own relationships, rather than its standing with President Trump. (Senate TV/Reuters)

We must respect his authority and constitutional responsibilities. We must, where we can, cooperate with him. But we are not his subordinates. We don’t answer to him. We answer to the American people.

And with that, mark Sen. John McCain (R-Ariz.) down as the second Republican senator to call on his colleagues to be a bulwark against President Trump. (The first being his Arizona colleague Sen. Jeff Flake.)

On Friday, McCain published an op-ed in The Washington Post contrasting Trump's tepid response to white supremacists in Charlottesville with his own (“There is nothing in their hate-driven racism that can match the strength of a nation conceived in liberty”), justifying his surprise “no” vote on Republicans' attempt to repeal Obamacare, calling on congressional leaders to compromise with Democrats and vice-versa, and basically advising all of Congress to prioritize its own relationships over its standing with Trump:

[W]e have to respect each other or at least respect the fact that we need each other. That has never been truer than today, when Congress must govern with a president who has no experience of public office, is poorly informed and can be impulsive in his speech and conduct.

In short, McCain just published 750 words in a national newspaper that seemed designed to jab directly at the president while rallying GOP resistance against him for the sake of the country.

After President Trump's most recent rhetoric about Charlottesville inflamed even more criticism, many Republicans stayed silent. But a handful of GOP lawmakers and now Trump's own economic adviser are directly criticizing him. (Jenny Starrs/The Washington Post)

It isn't a surprise that McCain feels this way about Trump, nor that he'd say as much publicly. McCain has been Trump's chief antagonist in the Senate pretty much since Trump was inaugurated.

The senator has publicly disagreed with Trump on renegotiating NAFTA (“facts are stubborn things”), on whether to bring back waterboarding (“The law is the law. We are not bringing back torture in the United States of America”) and on Trump's choice of Rex Tillerson for secretary of state (“There's also a realistic scenario that pigs fly,” McCain said when asked if he'd vote to confirm Tillerson). And, of course, there's Russia. While Trump has blasted the parallel investigations in Congress and at the FBI as a witch hunt, McCain has gone on TV alongside Senate Minority Leader Charles E. Schumer (D-N.Y.) to ask for more.

After McCain won the Arizona Republican primary a year ago, it took him precisely one day to ditch Trump. The ironic thing for McCain is that he campaigned for a sixth Senate term by pitching himself to voters as a bulwark against the president — specifically a President Hillary Clinton.

Now he's fulfilling that promise for a very different reason.

It also makes sense that McCain would speak out now. On Tuesday, Congress comes back from its summer break and faces a mountain of work to keep the government open and avoid a potential government default. Trump, a total wild card, has the power to derail negotiations, budget experts warn, by demanding that any budget have a down payment on his border wall.

A week ago, Trump went to McCain's back yard and, without mentioning the senator by name, expressed his exasperation with McCain's “no” vote that helped kill the Obamacare repeal.

President Trump issued scathing attacks against Arizona's senators during his Phoenix rally on Aug. 22, but said, "I will not mention any names. Very presidential." (The Washington Post)

McCain is also in a season of speaking his mind more than usual. Over the summer, he announced that he had a deadly form of brain cancer. Not even a week later, he came back to the Senate to vote against the repeal of the Affordable Care Act and to give a no-holds-barred lecture to the other 99 members about how their pride, partisanship and secretiveness have broken Congress.

In that speech, he opened the door for this week's op-ed, a more direct break from Trump:

We are an important check on the powers of the executive. Our consent is necessary for the president to appoint jurists and powerful government officials and in many respects to conduct foreign policy. Whether we are of the same party, we are not the president’s subordinates. We are his equal!

Sen. John McCain (R-Ariz.) on July 25 addressed senators days after being diagnosed with brain cancer. He said the Senate has become too partisan. (U.S. Senate)

McCain is not the first congressional Republican to step out in front of the president and throw his arms up. A month ago, Flake published and heavily promoted a book that casts Trump as the manifestation of a conservative movement with its head stuck in the sand.

“To carry on in the spring of 2017 as if what was happening was anything approaching normalcy required a determined suspension of critical faculties,” Flake wrote, “and tremendous powers of denial.”

What does this all mean? Well, two senators from a rising swing state ditching Trump doesn't a revolt make.

A new Fox News poll shows McCain's weakness with the very Republicans he's speaking to. He has a 55 percent favorable rating among registered voters, but he's underwater with Republican voters: 44 percent approve of him, while 52 percent don't. (Meanwhile, 65 percent of Democrats have a favorable view of McCain.)

Who knows if there will be more senators to follow McCain and Flake's lead. But if there are, we could look back on their anti-Trump arguments, laid out seven months into Trump's presidency, as one of the turning points.