“It’s not easy to debate a liar,” complained an email from one observer of the first presidential debate — and there was no question about which candidate he meant. Prevarication, falsification, fabrication are all familiar tactics that have been employed by Mitt Romney without much consequence to him ever since he entered public life, thanks to the inviolable taboo in the mainstream media against calling out a liar (unless, of course, he lies about sex).

Yes, President Obama ought to have been better prepared for Romney’s barrage of blather and bull. The Republican’s own chief advisor, Eric Fehrnstrom, had glibly described the “Etch-a-Sketch” strategy they would deploy in the general election, to make swing voters forget the “severe conservative” of the primaries. Romney executed that pivot on Wednesday night, but he could do so only by spouting literally dozens of provably fraudulent assertions — which various diligent fact-checkers proceeded to debunk.

Knowing that he is vulnerable on taxation and the budget for many reasons, including his own peculiar and secretive tax history, Romney made several contradictory claims regarding his economic plan. He has no plan to lavish $5 trillion in tax breaks on the wealthy. He won’t cut taxes for the rich at all. He vowed to provide tax relief to the middle class and won’t increase their tax burden. He swore that his tax cuts would not increase the deficit.

Finally, he said that with all of that, he would grow the economy enough to shrink and eventually eliminate the deficit — without raising taxes on anyone. And he claimed that there are several studies proving he can fulfill all of these conflicting promises — even though he refuses to provide any specific tax proposals beyond a broad tax cut.

There is no study proving that Romney can do what he promised, and among his lies is his description of editorials in the Wall Street Journal as “studies” of his plan. The most complete and unrefuted study of his claims remains the Tax Policy Center’s bipartisan report on the Romney plan, which shows that there is simply no way to pay for his $5 trillion, across-the-board tax cut without raising taxes on the middle class. None of the alternative studies he has cited proves otherwise — and some of them actually amass additional evidence that he is wrong.

Undoubtedly he knows all that. He knows that eliminating the estate tax, a mainstay of his plan, will benefit the rich enormously and almost nobody else.

He also knows that when he claims economic growth alone will erase the deficit, without raising taxes, he is inventing impossible numbers. As The National Memo’s Howard Hill demonstrated yesterday, the assumptions behind his claims are ridiculous. For the numbers to work, he would have to create not 12 million jobs, as he promised to do by 2016, but 162 million — more than the total current U.S. workforce. Or else the jobs created would have to pay more than $443,000 per year on average, which is even less likely than Rafalca winning the dressage medal at the next Summer Olympics.

At the same time, Romney accused the president of increasing the federal debt by an amount that is “almost as much … as all prior presidents combined.” This charge, which he leveled before, is patently false and by now Romney must know it. The prior debt, mostly run up by George W. Bush and his Republican congressional cronies, stood above $10 trillion when Obama took office. The debt is now just over $16 trillion, mostly due to costs incurred by Bush and by Obama’s successful effort to prevent a Depression.

Having essentially disavowed the health care reforms that were his sole significant achievement in his single term in elected office, the former Massachusetts governor suddenly claimed ownership of Romneycare. Presumably, this will make him more appealing to swing voters, too. But he still wants to do away with Obamacare, except for the parts that are popular.

For this maneuver, he must misrepresent his own proposed federal health care overhaul. He says there will be no change to Medicare for current beneficiaries, but repealing the Affordable Care Act will deprive them of free preventive care, increase their costs for prescription drugs and do irreparable harm to Medicaid, which provides assisted care for nine million destitute Medicare patients.

But Romney has been lying about the Affordable Care Act for years, according to his own former advisor Jonathan Gruber, the chief intellectual architect of Romneycare. Nearly a year ago, Gruber complained that Romney’s attempt to draw a sharp distinction between the Massachusetts legislation and Obamacare was phony. He told Capital New York in November 2011 that “they’re the same fucking bill. He just can’t have his cake and eat it too. Basically, you know, it’s the same bill. He can try to draw distinctions and stuff, but he’s just lying.”

Lying again? Indeed, the falsehoods flowed on every conceivable subject. Concerning energy, Romney claimed that “about half” of the renewable energy firms that received federal assistance under Obama administration programs went bankrupt — a claim that cannot be justified by any measure. Of the 28 firms that got federal loans or loan guarantees, three went under, representing less than 11 percent — and less than 5 percent of the funds committed. (This assertion was so blatantly untrue that the Romney campaign withdrew it the next day.)

The examples cited above hardly exhaust the deep well of dishonesty in the Republican campaign. What Romney has done presents a fundamental challenge to the American political media. Will news outlets hold him accountable for baldly misleading voters? Are they capable of confronting his continuous mendacity with basic facts? Some have made a beginning, while others have scarcely tried. If that isn’t their responsibility, then they no longer have any purpose at all.