Right before our eyes, American conservatism is becoming something very different from what it once was. Yet this transformation is happening by stealth because moderates are too afraid to acknowledge what all their senses tell them.

Last week’s Supreme Court oral arguments on health care were the most dramatic example of how radical tea partyism has displaced mainstream conservative thinking. It’s not just that the law’s individual mandate was, until very recently, a conservative idea. Even conservative legal analysts were insisting it was impossible to imagine the court declaring the health-care mandate unconstitutional, given its past decisions.

So imagine the shock when conservative justices repeatedly spouted views closely resembling the tweets and talking points issued by organizations of the sort funded by the Koch brothers. Don’t take it from me. Charles Fried, solicitor general for Ronald Reagan, told The Washington Post’s Ezra Klein that it was absurd for conservatives to pretend that the mandate created a market in health care. “The whole thing is just a canard that’s been invented by the tea party . . .,” Fried said, “and I was astonished to hear it coming out of the mouths of the people on that bench.”

Staunchly conservative circuit judges Jeffrey Sutton and Laurence Silberman must have been equally astonished, since both argued that overturning the law would amount to judicial overreach. Yet moderate opinion bends over backward to act as if this is an intellectually close question.

Similarly, House passage of Rep. Paul Ryan’s budget, with its steep cuts in the tax rates on the wealthy and sweeping reductions in programs for the poor, is an enormous step rightward from the budget policies of Ronald Reagan and George H.W. Bush. Faced with growing deficits, Reagan and Bush both supported substantial tax increases.

A small hint of how this push to the right moves moderates away from moderation came in an effort last week to use an amendment on the House floor to force a vote on the deficit-reduction proposals offered by the commission headed by former Sen. Alan Simpson and Erskine Bowles, former chief of staff to Bill Clinton.

You learned only in paragraphs buried deep in the news stories that the House was not even asked to consider the actual commission plan. To cobble together bipartisan support, sponsors of the ersatz Simpson-Bowles amendment kept all of the commission’s spending cuts but slashed the amount it prescribed for tax increases in half. See how relentless pressure from the right turns self-styled moderates into conservatives? If there’s a cave-in, it’s always to starboard.

Note how many deficit hawks regularly trash President Obama for not endorsing Simpson-Bowles while they continue to praise Ryan — even though Ryan voted to kill the initiative when he was a member of the commission. Here again is the double standard that benefits conservatives, proving that, contrary to establishment opinion, Obama was absolutely right not to embrace the Simpson-Bowles framework. If he had, a moderately conservative proposal would suddenly have defined the “left wing” of the debate, just because Obama endorsed it.

This is nuts. Yet mainstream journalism and mainstream moderates play right along.

A brief look at history suggests how far to the right both the Republican Party and contemporary conservatism have moved. Today’s conservatives almost never invoke one of our most successful Republican presidents, Dwight D. Eisenhower, who gave us, among other things, federally guaranteed student loans and championed the interstate highway system.

Even more revealing is what Robert A. Taft, the leader of the conservative forces who opposed Eisenhower’s nomination in 1952, had to say about government’s role in American life. “If the free enterprise system does not do its best to prevent hardship and poverty,” the Ohio Republican senator said in a 1945 speech, “it will find itself superseded by a less progressive system which does.” He urged Congress to “undertake to put a floor under essential things, to give all a minimum standard of decent living, and to all children a fair opportunity to get a start in life.”

Who can doubt that today’s right would declare his day’s Mr. Republican and Mr. Conservative a socialist redistributionist?

If our nation’s voters want to move government policy far to the right, they are entirely free to do so. But those who regard themselves as centrist have a moral obligation to make clear what the stakes are in the current debate. If supposed moderates refuse to call out the new conservatism for the radical creed it has become, their timidity will make them complicit in an intellectual coup they could have prevented.

ejdionne@washpost.com