A year or two ago, if you'd told me that Barack Obama would be leading John McCain by a seemingly comfortable margin with two weeks to go and asked me what, in their desperation, the Republicans would be talking about to try and scare my fellow Americans into voting against him, I'd have said race. After all, Republicans have race-baited in one form or other in most of our presidential contests since Richard Nixon's time, so it would have seemed impossible to me that they'd miss the chance to do so at a time when Democrats had actually gone to the trouble of nominating an African-American candidate.

It's true that we're hearing racial-code talk here and there. But the main fear tactic being employed now is something else. It's that Obama and his associates - and for that matter his supporters and even the regions of the country that he's destined to carry - are anti-American.'

Last Friday, in North Carolina, Sarah Palin told a rally that she was proud to be "with all of you hard-working, very patriotic, um, very, um, pro-America areas of this great nation". She means here of course that there are anti-American areas of America, and they are where the liberals live, and the people there are voting for Mr Anti-America.

This was especially interesting coming from a woman whose husband, Todd Palin, was until just six years ago an enrolled member of a rightwing fringe political party that wanted the state of Alaska to secede from the US. But if you understand rightwing logic, then you'd know that Mr Palin had no choice but to join the Alaska Independence party in 1995, because by that time the America he thought he knew and loved had been brought to ruin by the liberals and socialists and America-haters. See?

Likewise, earlier this month, Joe McCain, the brother of John, said that Alexandria and Arlington, the two major cities in the northern Virginia suburbs that lie just across the Potomac River from Washington, were "communist country" as far as he was concerned. His brother lives in Arlington when in the nation's capital for work, and his brother's campaign is headquartered there as well, but never mind. A McCain spokeswoman offered a wan apology at the time, but lo and behold, just last Saturday a different McCain spokes-woman said on television that while Obama would perform well in northern Virginia, "the rest of the state - real Virginia if you will - I think will be very responsive to Senator McCain's message". This did not seem a planned one-liner. The spokeswoman made the fatal error of saying what she actually thinks. Republican Virginia equals real Virginia. Democratic Virginia is alien and impure.

Do you folks do this sort of thing in Britain? I know there's something about the chap on the Clapham omnibus who's supposed to represent some kind of middling everyman. And I know you've got your xenophobes just like we do. But trust me. You don't have a right wing that's anything like our right wing.

This point was proved most dramatically by a woman named Michele Bachmann, a member of Congress from Minnesota. In an interview last Friday on Hardball, a leading US cable talk show, host Chris Matthews asked Bachmann whether Obama worried her. "Absolutely. I'm very concerned that he may have anti-American views," she said. He asked her what she thought distinguished liberal from hard left from anti-American. If she maintains such distinctions in her mind, she refused to acknowledge them. Then, finally, Matthews - who deftly fed her the rope to hang herself - asked her how many members of the US Congress held, in her view, anti-American views.

It's been almost a two-year campaign. There have been moments we've thought of as memorable, only to see the tide of events erase their mark from the sand. Bachmann's answer, however, will live imperishably: "What I would say - what I would say is that the news media should do a penetrating exposé and take a look. I wish they would. I wish the American media would take a great look at the views of the people in Congress and find out, are they pro-America or anti-America? I think people would love to see an exposé like that."

Before we go any further - who is this Bachmann? She's a first-term backbencher from exurban Minneapolis who says the Lord told her to run for Congress. She declared herself "a fool for Christ" in 2006 when she announced her candidacy. By all accounts she's down with the whole rightwing Christian package: immigrants bring disease and pestilence, homosexuals want to indoctrinate straight children, and so on. Republican leadership undoubtedly pushed her out on to television because she is, as you Brits say, a looker - at least by the standards of Congress.

The call for an investigation into the beliefs of every federal lawmaker, and an exposé of those found wanting in their patriotism, certainly takes us into deeply creepy territory. I would not call Bachmann herself a fascist. Odd as it sounds, to do so would be to grant her far too much credit. For one to embrace an -ism, even a repugnant one, one needs to have read a certain amount of history and political philosophy. Bachmann is just an idiot. She wouldn't know Edmund Burke from Billie Burke (she played the good witch in the Wizard of Oz), and she obviously has no idea that, in her rejection of the two bedrock American principles of separation of church and state and freedom of thought, she is the one who is as anti-American as they come.

But friends, all is not darkness. Bachmann's appearance caused a national uproar. Colin Powell, in endorsing Obama yesterday, said of Bachmann's comments that "we have got to stop this kind of nonsense and pull ourselves together". Her Democratic opponent raised nearly half a million dollars from around the country in just 24 hours, and he now has a chance of beating her.

That would be nice. But let's go back to the big contest. With Bachmann, the lid came off the rightwing id. It will happen many more times over these next two weeks. McCain, now openly using the word "socialist" to describe Obama's proposals (the week after his friend George W Bush took federal control of nine major banks!), and especially Palin have shown every sign of encouraging it. Their goal is to scare Americans about Obama, but moderate, independent voters might well decide that Obama looks a lot less scary than they do.

•Michael Tomasky is editor of Guardian America

michael.tomasky@theguardian.com