Four years ago, when I was writing about the 2008 presidential campaign, I wrote with dismay and surprise at the spate of falsehoods coming out of John McCain's campaign for president. McCain had falsely accused his opponent Barack Obama of supporting "comprehensive sex education" for children, and of wanting to raise taxes on the middle class, while his running mate, Alaska Governor Sarah Palin, took credit for opposing the so-called "Bridge to Nowhere", which she had actually supported.

At the time, such false and misleading claims from a presidential candidate seemed shocking: they crossed an unstated line in American politics – going from the usual garden-variety campaign exaggeration to wilful lying.

Ah, those were the days … after watching Mitt Romney run for president the past few months, he makes John McCain look like George Washington (of "I Can't Tell A Lie" fame).

Granted, presidential candidates are no strangers to disingenuous or overstated claims; it's pretty much endemic to the business. But Romney is doing something very different and far more pernicious. Quite simply, the United States has never been witness to a presidential candidate, in modern American history, who lies as frequently, as flagrantly and as brazenly as Mitt Romney.

Now, in general, those of us in the pundit class are really not supposed to accuse politicians of lying – they mislead, they embellish, they mischaracterize, etc. Indeed, there is natural tendency for nominally objective reporters, in particular, to stay away from loaded terms such as lying. Which is precisely why Romney's repeated lies are so effective. In fact, lying is really the only appropriate word to use here, because, well, Romney lies a lot. But that's a criticism you're only likely to hear from partisans.

My personal favorite in Romney's cavalcade of untruths is his repeated assertion that President Obama has apologized for America. In his book, appropriately titled "No Apologies", Romney argues the following:

"Never before in American history has its president gone before so many foreign audiences to apologize for so many American misdeeds, both real and imagined. It is his way of signaling to foreign countries and foreign leaders that their dislike for America is something he understands and that is, at least in part, understandable."

Nothing about this sentence is true.

President Obama never went around the world and apologized for America – and yet, even after multiple news organizations have pointed out this is a "pants on fire" lie, Romney keeps making it. Indeed, the "Obama apology tour", along with the president bowing down to the King of Saudi Arabia, are practically the lodestars of the GOP's criticism of Obama's foreign policy performance (the Saudi thing isn't true either).

But foreign policy is a relatively light area of mistruth for the GOP standard-bearer. The economy is really where the truth takes its greatest vacation in Romney world. First, there is Romney's claim that the 2009 stimulus passed by Congress and signed by President Obama "didn't work". According to Romney, "that stimulus didn't put more private-sector people to work." While one can quibble over whether the stimulus went far enough, the idea that it didn't create private-sector jobs has no relationship to reality. According to the Congressional Budget Office, the stimulus bill created more than 3m jobs – a view shared by 80% of economists polled by the Chicago Booth School of Business (only 4% disagree).

Romney also likes to argue that the stimulus didn't help private-sector job growth, but rather helped preserve government jobs. In fact, the Obama years have been witness to massive cuts in government employment. While the private sector is not necessarily "doing fine", as Obama said in a recent White House press conference, it's doing a heck of a lot better than the public sector.

And the list goes on. Romney has accused Obama of raising taxes – in reality, they've gone down under his presidency, and largely because of that stimulus bill that Romney loves to criticize. He's accused the president of doubling the deficit. In fact, it's actually gone down on Obama's watch.

Romney took credit for the success of the auto bailout – even though he wrote an op-ed for the Washington Post titled "Let Detroit Go Bankrupt". He's said repeatedly that businesses in America see Obama as the "enemy", and that under his presidency "free enterprise" and economic freedom" are at risk of disappearing. In reality, since taking office, corporate profits, industrial production and the stock market are up, while corporate bankruptcies have actually decreased.

Then, there is the recent Romney nugget that the Obama administration passed Obamacare with the full knowledge that it "would slow down the economic recovery in this country" and that the White House "knew that before they passed it". It's an argument so clearly spun from whole cloth that according to Jonathan Chait, the acerbic political columnist for New York Magazine, Romney is "Just Making Stuff Up Now".

Also of Obamacare, Romney has said that it will lead to the government taking over 50% of the economy (not true) – its true cost can't be computed (that's why we have a Congressional Budget Office in the United States); that it will create to "a massive European-style entitlement" (many liberals wish this were true, but alas, it is not); and that it will lead to a government-run healthcare system (a lie so pervasive that it's practically become shorthand for Republicans – yet it too, like the infamous made-up death panels of the health care debate, is simply not accurate).

The lying from the Romney campaign is so out-of-control that Steve Benen, a blogger and producer for the Rachel Maddow show compiles a weekly list of "Mitt's Mendacity" that is chockfull of new untruths. Benen appears unlikely to run out of material any time soon, particularly since Romney persists in repeating the same lies over and over, even after they've been debunked.

This is perhaps the most interesting and disturbing element of Romney's tireless obfuscation: that even when corrected, it has little impact on the presumptive GOP nominee's behavior. This is happening at a time when fact-checking operations in major media outlets have increased significantly, yet that appears to have no effect on the Romney campaign.

What is the proper response when, even after it's pointed out that the candidate is not telling the truth, he keeps doing it? Romney actually has a telling rejoinder for this. When a reporter challenged his oft-stated assertion that President Obama had made the economy worse (factually, not correct), he denied ever saying it in the first place. It's a lie on top of a lie.

Now, it's certainly true that on the campaign trail, facts can be stretched in many different directions – and both parties, including President Obama, frequently make arguments that are misleading, lacking in context or simply false. But it is virtually unheard of for a politician to lie with such reckless abandon and appear completely unconcerned about getting caught.

Back in the old days (that is, pre-2008) it would have been considered unimaginable that a politician would lie as brazenly as Romney does – for fear of embarrassment or greater scrutiny. When Joe Biden was accused of plagiarizing British Labor Leader Neil Kinnock's speeches in 1988, it derailed his presidential aspirations. When Al Gore was accused of exaggerating his role in "inventing the internet" (which, actually, was sort of true), it became a frequent attack line that hamstrung his credibility. Romney has done far worse than either of these candidates – yet it's hard to discern the negative impact on his candidacy.

Romney has figured out a loophole – one can lie over and over, and those lies quickly become part of the political narrative, practically immune to "fact-checking". Ironically, the more Romney lies, the harder it then becomes to correct the record. Even if an enterprising reporter can knock down two or three falsehoods, there are still so many more that slip past.

It's reminiscent of the old line that a lie gets halfway around the world before the truth gets its boots on. In Romney's case, his lies are regularly corrected by media sources, but usually, in some antiseptic fact-checking article, or by Democratic/liberal voices who can be dismissed for their "partisan bent". Meanwhile, splashed across the front page of newspapers is Romney saying "Obamacare will lead to a government take-over of healthcare"; "Obama went on an apology tour"; or "the stimulus didn't create any jobs". Because, after all, it's what the candidate said and reporters dutifully must transcribe it.

Pointing out that Romney is consistently not telling the truth thus risks simply falling into the category of the usual "he-said, she-said" of American politics. For cynical reporters, the behavior is inevitably seen to be the way the political game is now played. Rather than being viewed and ultimately exposed as examples of a pervasive pattern of falsehoods, Romney's statements embed themselves in the normalized political narrative – along with aggrieved Democrats complaining that Romney isn't telling the truth. Meanwhile, the lie sticks in the minds of voters.

As MSNBC's Steve Benen told me:

"Romney gets away with it because he and his team realize contemporary political journalism isn't equipped to deal with a candidate who lies this much, about so many topics, so often."

Romney is charting new and untraveled waters in American politics. In the process, he is cynically eroding the fragile sense of trust that exists between voters and politicians. It's almost enough to make one pine for the days when Sarah Palin lied about "the Bridge to Nowhere".