Sens. Bob Corker (R-Tenn.), left, confers with Sen. Jeff Flake (R-Ariz.). (Win Mcnamee/Getty Images)

MICK MULVANEY, the phony deficit hawk President Trump tapped to oversee the nation’s budget, all but admitted on Sunday that the GOP tax plan currently before the Senate is built on fiction. Senators from whom the public should expect more — such as Susan Collins (R-Maine), Bob Corker (R-Tenn.), Jeff Flake (R-Ariz.), John McCain (R-Ariz.) and Lisa Murkowski (R-Alaska) — should finally denounce this nonsense.

Mr. Mulvaney, the head of the White House’s Office of Management and Budget, said on NBC’s “Meet the Press” that Republicans are trying to “game the system” by pretending that expensive tax cuts will expire in several years, arguing that the pretense is necessary to “shoehorn the bill into the rules” of the Senate. “A lot of this is a gimmick,” he said.

Yet those rules exist for a reason — to prevent senators from busting the federal budget. The Senate GOP bill would lower personal tax rates but schedule them to tick back up in future years. This maneuver cuts the plan’s nominal sticker price to $1.5 trillion. But Mr. Mulvaney and other Republicans reason that, once written into the law, Congress would not allow these provisions to sunset. So the Senate Republican tax plan would cost $1.5 trillion on paper — already too much — but a lot more in reality.

This is just one indication that the plan directly contradicts the specific promise Mr. Corker made to oppose any tax bill that would “add one penny” to the deficit, not to mention the general concern that other lawmakers have expressed about the nation’s deteriorating finances.

The House speaker fails to account for what happens after 2018 in his estimate for Cindy, an example voter. (Meg Kelly/The Washington Post)

Mr. Mulvaney and many other Republicans argue that the bill’s tax cuts would spur economic growth, in turn increasing federal revenue, and therefore pay for themselves. No credible analysis substantiates this fantasy. But there are many that predict fiscal ruin. The nonpartisan Tax Policy Center released one Monday. Assessing the House version of the plan and accounting for the economic growth its tax cuts would induce, the analysts found that growth would offset only about 12 percent of the plan’s cost over the first decade. After an initial economic boost, bigger deficits and rising interest rates would drag on the economy.

Attempting to brush away concerns about the numbers, Mr. Mulvaney said Sunday, “What you should really be looking at is the policies themselves. And we think these are excellent policies.” In fact, the Senate bill would load up on debt to provide upper-income tax breaks that no serious assessment would put on a list of national priorities. Curbing the estate tax, for example, would do little other than enrich well-off heirs. Though dropping the corporate tax rate could make the United States a somewhat more attractive place to do business, it is not worth adding substantially to the debt.

This is a gut-check moment for any senator who has ever claimed to care about the debt. The Senate is on the verge of further burdening future generations that already face a big bill from decades of budgetary recklessness. The GOP tax bill is a charade. In case anyone thought otherwise, Mr. Mulvaney just confirmed it.