posted February 01, 2017 12:45 PM            

The maverick is unleashed.

Sen. John McCain, famously independent-minded and fresh from his own resounding re-election victory, has served notice that he is the Republican lawmaker most willing to defy the new Republican president.

Some fret over how to handle their disagreements with Donald Trump; Mr. McCain exhibits no such uncertainty.

In just over a week’s time, Mr. McCain has called the new Trump ban on immigration from a set of Muslim-majority countries a recruiting boon for Islamic State radicals; threatened to codify Russian economic sanctions into law to prevent Mr. Trump from lifting them; called the president’s decision to withdraw from the Trans-Pacific Partnership “a serious mistake”; and called the idea of imposing a 20% tariff on imports from Mexico to pay for a border wall “insane.”
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The senator also served notice that he will fight any effort to reinstate waterboarding or other forms of torture in interrogation of terror suspects; and declared he may oppose the Trump nominee for budget director because of his past opposition to military spending and troop deployments in Afghanistan.

In short, frenetic as the new president has been, Mr. McCain is matching him step for step. Thus is a president willing to go rogue being matched by a powerful lawmaker—head of the Armed Services Committee and former GOP presidential nominee—prepared to do the same.

“The main thing is, do the right thing,” Mr. McCain said in an interview. “I feel, frankly, a greater burden of responsibility. The world’s on fire, we have more challenges than any time in the last 70 years and, with the chairmanship of the Armed Services Committee and whatever influence I have, I need to exercise it because the responsibilities are so great.”

Mr. McCain said he is willing to work with Mr. Trump: “I believe there are areas where we certainly can.” In fact, he will be crucial to the president’s desire to ramp up military spending and overhaul defense procurement practices, areas where they are almost entirely in sync.

Plus, he said he has good relations with key Trump security aides: Defense Secretary Jim Mattis, Homeland Security Secretary John Kelly and national security adviser Michael Flynn. White House chief of staff Reince Priebus, he noted, was Wisconsin chairman of his 2008 presidential bid, and he has traveled abroad on congressional delegations with Vice President Mike Pence.

But, he said, he has no communication going with the president himself.

This is a potentially serious long-term problem for Mr. Trump. The president is not especially susceptible to criticism from Democrats, which is predictable and easily dismissed, but opposition from Republicans, who control both chambers and every committee of Congress, and thereby the Trump agenda, is far more important.

Republicans have few votes to spare with their 52-48 majority in the Senate, so the White House has little margin for error within the party there. Though Mr. McCain’s ability to unite Republicans behind him has long been questionable, Mr. Trump could ill afford it if Republican misgivings coalesced around a highly visible leader.

The bad blood isn’t surprising. Early in the 2016 presidential campaign, Mr. Trump belittled Mr. McCain’s horrific Vietnam War experience, during which his Navy attack jet was shot down and, while seriously injured, he spent more than five years in a North Vietnamese prison.

“He’s not a war hero,” Mr. Trump said. “He’s a war hero because he was captured. I like people who weren’t captured.”

The comment came early in the Trump campaign, and many thought it would derail it. The fact it didn’t was a key initial sign of how much the GOP had changed.

Mr. McCain also noted that Breitbart News, the site previously overseen by top Trump adviser Stephen Bannon, has “attacked me incessantly for years.”

All that leaves lots of room for bad blood. Some of the disagreements are local. Mr. McCain argues that the North American Free Trade Agreement, which Mr. Trump wants to renegotiate, has benefited his home state of Arizona, and that the tariff on Mexican imports floated by the White House clearly would hurt it.

His own war experience with brutal treatment during incarceration leaves him starkly at odds with Mr. Trump’s belief that waterboarding and other forms of harsh interrogation are acceptable.

But the area that seems to most bother Mr. McCain isn’t personal; it is a seemingly deep disagreement with the new president over his desire to strengthen ties with Russian President Vladimir Putin.

The last two American administrations, of George W. Bush and Barack Obama, similarly started “with the mistaken belief there would be improved relations with a hardened KGB colonel,” Mr. Putin, only to be disappointed, he said.

“The difference now versus before is he’s invaded a country”—Ukraine—and, he added, has tried to influence an American election.

Corrections & Amplifications
Michael Flynn is national security adviser in the White House. An earlier version of this article incorrectly stated that Michael Kelly holds the position. (Jan. 30, 2017)