Sen. John McCain of Arizona joined 50 fellow Republicans on Friday night in voting yes on a Senate bill that slashes taxes on corporations and billionaires, while enacting the largest tax increase in history on many poorer Americans.

That McCain supports such policies is no surprise, given his ideological history. However, his vote is shocking nonetheless in its flagrant violation of all the values McCain claimed to hold just a few months ago.

Senators received the tax bill hours before voting, in an unsearchable version so new that it had handwritten changes. Members learned of possible amendments from lobbyists. There were no regular committee hearings or any attempts whatsoever to involve Democrats.

There may be no historical precedent for jamming through a bill of such significance in this manner – except the chamber’s efforts this past July and September to repeal the Affordable Care Act. But in those instances, McCain loudly proclaimed he could not vote for those bills because of his devotion to regular order in the Senate.

McCain returned to Washington in late July soon after being operated on for brain cancer in order to vote on the first GOP health care bill and delivered a dramatic speech that CNN called “a Washington moment for the ages.”

“As I stand here today,” McCain declared, “I have a refreshed appreciation for the protocols and customs of this body.”

It was wrong, he said, to force through “social and economic change” that was “massive” without any support from across the aisle. Republicans were trying to do this “by coming up with a proposal behind closed doors in consultation with the administration, then springing it on skeptical members.”

So, McCain said, “Let’s return to regular order … the old way of legislating in the Senate, the way our rules and customs encourage us to act.” The Senate’s traditions were “deliberately intended to require broad cooperation to function well at all.”

He then concluded with a stirring paean to slow, deliberative lawmaking, asking, “What greater cause could we hope to serve than helping keep America the strong, aspiring, inspirational beacon of liberty and defender of the dignity of all human beings and their right to freedom and equal justice?”

To McCain’s credit, he then did vote against the Republican health care bill shortly afterward. And his announcement in September that he would not support another GOP run at the American Care Act led to Majority Leader Mitch McConnell shelving the issue indefinitely.

In the interim, McCain took the time to again express his dedication to Senate traditions and bipartisan compromise in a Washington Post op-ed.

“We seem convinced that majorities exist to impose their will with few concessions,” he wrote. But this was dangerous: “We might not like the compromises regular order requires, but we can and must live with them if we are to find real and lasting solutions. And all of us in Congress have the duty, in this sharply polarized atmosphere, to defend the necessity of compromise before the American public.”

In particular, McCain said, “Let’s try it on tax reform.” This would “prove the value of the United States Congress to the great nation we serve.”

McCain clearly now feels some sensitivity about his shameless about-face. “I have called for a return to regular order,” he weakly explained in a statement about his support for the tax bill, “and I am pleased that this important bill was considered through the normal legislative processes, with several hearings and a thorough mark-up in the Senate Finance Committee during which more than 350 amendments were filed and 69 received a vote.”

For anyone who understands Senate procedure, this is meaningless. “Citing filed amendments is deeply cynical and shows that he doesn’t really care about regular order,” says Adam Jentleson, former deputy chief of staff for Nevada Democrat and one-time Senate Majority Leader Harry Reid. “He just used it because it’s a big number, and he thinks no one will call him on it. … It could be a million amendments filed but that doesn’t mean any of them received real consideration.”

And it’s simple even for non-experts to judge McCain’s sincerity. The Senate Finance Committee debated the bill for a mere four days and passed it on a party line 14-12 vote. By comparison, the same committee conducted 33 days of hearings on the comparable Tax Reform Act of 1986 — in 1985, a year before the vote — followed by a subsequent month of drafting meetings. Eventually, the bill was unanimously approved by the Finance Committee and subsequently passed the entire Senate in mid-1986 by a vote of 97-3 after three weeks of floor debate.

It’s impossible to know McCain’s true motives, of course, and his office did not immediately respond to a request for comment. But the tax bill does differ from the attempts to repeal the Affordable Care Act in one key aspect: It directly benefits McCain and his family in obvious ways. His wife Cindy McCain’s estimated $100 million fortune is largely based in her ownership of liquor distributor Hensley Beverage, which would gain from the bill’s cut to alcohol taxes. It also will allow the McCain children to inherit $22 million tax-free, doubled from the $11 million exemption under current law.