PAUL RYAN wants to tell you about the wonders of the 20 percent cut in tax rates that he and running mate Mitt Romney propose. He doesn’t want to tell you how much it will cost. On Sunday, Fox News’s Chris Wallace asked the Republican vice presidential nominee this basic question four times, citing projections of a 10-year cost of $5 trillion. Four times, Mr. Ryan dodged, hiding behind a flimsy scaffolding of pseudo-wonkiness. “Look, I won’t give you a baseline with these because that’s what a lot of this is about,” he said.

The $5 trillion figure derives from an estimate by the nonpartisan Tax Policy Center that the Romney tax cuts — without base-broadening offsets — would reduce revenue by $456 billion in 2015. Multiply by 10, and account for costs rising each year, and the $5 trillion estimate is probably low.

If Mr. Ryan wants to hide behind jargon, here’s a relevant point. “Baseline” refers to the assumptions made about the budget if the Romney-Ryan tax cut isn’t enacted. The Tax Policy Center’s baseline is favorable to the Republican plan because it assumes the extension of all Bush tax cuts. A more realistic, or at least equally plausible, set of assumptions would add another $1 trillion to its cost. Mr. Ryan flings about terms such as “baseline” to obscure that painful fact.

The Republican ticket says it could pay for its tax cut by eliminating loopholes. But the biggest loopholes are popular: the exclusion from taxation of employer-sponsored health insurance and the deductions for mortgage interest, charitable contributions and state and local taxes. Pressed by the assiduous Mr. Wallace about which of these Mr. Ryan would limit, the nominee pleaded a lack of time. “It would take me too long to go through all of that,” he said.

The GOP wants voters to think that only the rich would be affected by its loophole closing. “And don’t forget that the higher-income people have a disproportionate amount of the loopholes that they use,” Mr. Ryan said. Well, actually, no. Higher-income people reap a “disproportionate amount” of the benefit of lower rates on capital gains and dividends — households earning more than $200,000 a year receive 90 percent of the benefit. But the Romney-Ryan plan would leave that break in place. Most of the remaining major tax breaks flow primarily to households earning $200,000 or less. For example, more than two-thirds of the benefit of the deduction for home mortgage interest goes to those making less than $200,000 a year.

Finally, if you heard a glimmer of responsibility from Mr. Romney lately, think again: Mr. Ryan pulled back on it. Mr. Romney has been saying that middle-class families shouldn’t expect their tax bills to go down very much, if at all, because their lower rates would be offset by, yes, curtailing deductions. Fox News’s Neil Cavuto pressed Mr. Ryan on that score. “Was he trying to brace us for some bitter news?” Mr. Cavuto asked. Mr. Ryan: “No, not at all. . . . Middle income taxpayers get higher take-home pay.”

Mr. Wallace asked what Mr. Romney’s priority would be if his numbers didn’t add up and the reduction in tax rates couldn’t be done without losing revenue. Mr. Ryan didn’t flinch. “Keeping tax rates down,” he replied.

In other words, revenue-neutral would be nice. Lowering tax rates is the Republican priority, deficits be damned.