Attractive, humorous and articulate, she had been a tough, honest and effective governor of Alaska, but she was destroyed by a hostile media who ridiculed what they saw as rural redneckery and mercilessly exposed her lack of intellectual depth, knowledge of a wider world and occasional flakiness. Independent voters panicked and she became a liability.
Mitt Romney is a cautious man and had been expected to make a safe pick for vice-president. Yet he opted for the quirky, brilliant, likeable, intellectual dynamo that is Paul Ryan, whose passion for small government, fiscal conservatism and individual responsibility rather than state dependency has the Republican heartlands swooning.
A congressman since 1999, as Chairman of the House Budget Committee Ryan, 42, is notorious in Washington as a radical reformer who came up with a proposed budget that would reshape and cut federal spending to a level that the US could actually afford. "I love good ideas," he has said. "I love the competition of ideas, I love debating ideas -- and in my mind, in what I do, it's about ideas that make life better for people."
To those who believe welfare benefits are sacrosanct and can be financed by tax increases, Ryan is nothing but a heartless ideologue. After polls showed even independents responding positively to his charm and his thoughtful speeches, the hysterical Maureen Dowd of the New York Times outdid herself last week when she described him as "Scrooge disguised as a Pickwick". He "should stop being so loveable. People who intend to hurt other people should wipe the smile off their faces".
Democratic political ads are already showing Ryan pushing grannies over cliffs, yet he's unapologetic and on the offensive. The budget for Medicare (healthcare for the over-65s), he argues, has been raided to the tune of $716m to finance the eye-wateringly expensive Obamacare.
A Romney government would abolish Obamacare, save Medicare from going broke and look after granny. The US needs to rediscover the self-reliance and can-do that made it great, rather than allowing big government to wreck its national ethos and economy.
Earlier this year Sarah Palin memorably asked an audience: "How's that hopey, changey thing workin' out for you?" The truth is that with low growth, high unemployment and catastrophic debt, it isn't too good for many.
Pre the arrival of Ryan, this was already a polarised election, with both camps desperate to motivate their base. Millions are being spent on vicious TV advertisements.
Four years ago, when he became the Democratic nominee, Obama said: "If you don't have any fresh ideas, then you use stale tactics to scare voters. If you don't have a record to run on, then you paint your opponent as someone people should run from. You make a big election about small things." The bleak truth is that the world is in economic turmoil, the Obama administration is out of ideas and it's running a relentlessly negative campaign concentrating on frightening people.
Obama has made huge concessions to illegal immigrants that will copperfasten the Hispanic vote. The incumbent Vice-President, Joe Biden, descended to the gutter last week when, in a Southern accent, he told an audience that was half African-American that a Romney White House would "unchain Wall Street. They're going to put y'all back in chains".
But the arrival of Ryan not only turns the election into a fight about big ideas. It has also galvanised the hitherto dull and ideologically volatile Romney, who seems to be enthusiastically following the intellectual leadership of his young running-mate and finding some fire in his own belly. Reeling from some truly vicious TV ads, Biden's racial dog-whistling made Romney lose his temper. "His [Obama's] campaign and his surrogates have made wild and reckless accusations that disgrace the office of the presidency. This is what an angry and desperate presidency looks like."
With unaccustomed eloquence, he went on: "Everywhere I go in America, there are monuments that list those who have given their lives for liberty. There's no mention of their race, their party affiliation or what they did for a living. They lived and died under a single flag fighting for a single purpose. They pledged allegiance to the United States of America. So, Mr President, take your campaign of division and anger and hate back to Chicago and let us get about rebuilding and reuniting America."
It's going to be a fascinating election. And this time the vice-presidential debates between two Catholic Irish-Americans might be where the really exciting action is. As one commentator put it, we're focusing now on the Robins rather than the Batmans.