Paul Ryan, the House speaker, sees the tax act as a bonanza for the working stiff: He tweeted that a public school secretary would see a whopping $1.50 a week extra in her paycheck. It’s touching that the secretary can now afford an extra McDonald’s coffee every week, but the deficit, thanks partly to the tax cut, is projected after years of decline to explode to a trillion dollars annually.

Tax cuts, regardless of the deficit, are an obsession with Republicans and a source of shameless hypocrisy. During the recent shutdown crisis, the House Freedom Caucus balked at a deal to avert an impasse because it contained additional domestic spending, while in the Senate, Rand Paul of Kentucky held up the vote because the spending creates debt that threatens “the livelihoods of our children.” Yet the senator and every single Freedom Caucus member enthusiastically had voted only a few weeks before for a fiscally irresponsible tax bill.

Republicans were once the party of conservation and the environment: from Abraham Lincoln, who set aside Yosemite for what later became a national park, to Theodore Roosevelt, preserving 230 million acres of public land, to Richard Nixon, who signed the Clean Air Act and created the Environmental Protection Agency.

Now the E.P.A. is being systematically gutted. Its administrator, Scott Pruitt, has named as chairman of its science advisory board a person who criticizes the E.P.A.’s standards for exposure to mercury (a neurotoxin causing severe brain damage) and believes ozone pollution rules are unnecessary because Americans spend most of their time indoors. Another of the board’s “alternative” scientists is a man who has stated that “modern air is a little too clean for optimum health.”

Republicans always counted themselves as strong supporters of law and order. Whenever a crime bill was considered in Congress, I used to joke with my colleagues that any minute, a Republican would offer an amendment proposing the death penalty for jaywalking. But the president’s high-decibel smear campaign against the professionals of the F.B.I. destroys the party’s pretense of being a friend of law enforcement, as does the administration’s dismantling of the Consumer Financial Protection Agency and its rules against consumer fraud. The fact that Mr. Trump and his senior appointees are scofflaws regarding conflict-of-interest statutes does not enhance their reputation as straight arrows.

So what do Republicans have left? The tax cut, the sole important legislation from the Republican Congress, shows that catering to its rich contributors is the party’s only policy. The rest of its agenda is simply tactics and trickery.

As the party has become unmoored from positive belief, it has grown manipulative, demagogic and contemptuous of truth. This was foreshadowed in 2004 when a senior adviser to George W. Bush boasted that “we create our own reality.” It has culminated in the president’s counselor Kellyanne Conway’s appealing to “alternative facts,” meaning lies, on behalf of her boss, who has made an average of 5.6 false or misleading claims a day since his inauguration.