Think about it this way: Bad monetary policy means a bad economy, which gives power back to the party that didn't have it before. And so long as the monetary problem gets fixed, the economy will too, and the new government's policies will, whatever their merits, get the credit. That's how ideology changes.
In 1896, for example, Republicans completed their transformation from being the anti-slavery party to the anti-inflation one. Back then, the U.S. was on the gold standard, but there wasn't enough gold. Miners had found so little of it that overall prices were falling, which was particularly bad news for anyone who'd borrowed money. That's because wages fall if prices do, so debts that don't become harder to pay back. The result was two decades of slower-than-it-should-have-been growth where the economy was in recession more often than not.
Democrats, for their part, finally came up with a solution: stop crucifying mankind on a cross of gold, and use silver as money, too. They were four years too late, though. Gold discoveries in South Africa in 1896 and the Yukon in 1898 made the gold standard sustainable just in time for the Republicans, who had become the party of the financial elite that stood to lose a lot of money from inflation, to rally to its defense. Wall Street threw more money, as a percent of gross domestic product, into defeating the pro-silver Democrats than has been spent in any presidential election before or since. And it worked. Republicans won, the gold standard survived, and a new old era of conservative politics, of balanced budgets and low inflation, was ushered in.
Well, at least until World War I. That's because Republicans agreed on fiscal and financial policy, but not on regulation. That split let Woodrow Wilson win a three-way race in 1912, and, despite getting reelected on the slogan that "he kept us out of war," he didn't in 1917. Now, gold had already been pouring into the U.S., fueling inflation, as people moved it out of Europe, but once we joined the Allies, we also partially suspended the gold standard by banning gold exports.
That left us with higher prices and a big pile of shiny rocks after the war ended. So, in 1920, the Fed raised rates so much that prices not only stopped rising, but actually started falling. A deep recession followed, right before the presidential election. That, together with general war weariness, was enough for an extreme mediocrity like Warren G. Harding to win the biggest popular vote victory, by percentage points, on record just on the strength of three word: return to normalcy. A year later, the Fed lowered rates, the Roaring Twenties were born, and the conservative orthodoxy of low taxes and low spending once again seemed to be vindicated.
It wouldn't for long. Households, you see, went on a borrowing binge in the 1920s. They borrowed money to buy cars. They borrowed money to buy homes. And, yes, they borrowed money to buy stocks. So once the market crashed, this pyramid of debt did too. Even zero interest rates weren't enough to stop the economy's free fall. This only got worse when people panicked, sometimes justifiably so, that all these bad debts would make their banks go bust. That became a self-fulfilling prophecy as people rushed to pull their money out before everyone else, and the Fed, which was more concerned about propping up the gold standard than propping up the financial system, let everything collapse.
The craziest part was that the U.S., along with France, had so much gold that they could have created inflation and still stayed on the gold standard if they wanted to. But they didn't. They were so pathologically afraid of anything even resembling inflation that they chose depressions that forced them off gold instead. Hoover tried to run balanced budgets in the face of 25 percent unemployment, and the Fed raised rates in the face of bank runs, all to try to maintain the gold standard that, to them, was synonymous with civilization. This wasn't exactly popular. FDR came in and immediately did everything Hoover hadn't been willing to: going off gold, stress testing the banks, and spending money even if it meant running deficits. Recovery followed, and, in the process, discredited laissez-faire government for more than a generation.
By the 1970s, though, the Fed had made the opposite mistake of the one it made in the 1930s. This time, instead of saying there was nothing it could do about falling prices, it said there was nothing it could do about rising prices. Part of it was because Richard Nixon pressured it not to raise rates before his reelection. Another part was that the oil shocks pulled it in opposite directions—higher oil prices hurt the economy, but also increased inflation—and it didn't know what to do. And the final part was that widespread cost-of-living-adjustment contracts turned price shocks into wage shocks that then made the price shocks even worse. Now, even though this didn't have anything to do with actual Keynesianism, which, remember, is when the government runs deficits to fight recessions, "Keynesianism" became the bête noire of stagflation.
It was more than enough to undo Jimmy Carter, who had the misfortune of appointing the right Fed Chair at the wrong time, at least for him. Paul Volcker, you see, tried raising rates in 1980, just enough to create a small recession, before really raising them in 1981 and whipping inflation for good at the cost of a much deeper recession. This was perfectly timed, though, for Ronald Reagan, who got to run against Carter during a slump, and then watch Volcker engineer an inflation-killing slump that ended just in time for his own reelection. You know the rest of the story: it looked like government really was the problem, not the solution, and now it was Morning in America, etc., etc.
Now, it's worth pointing out that politics can change without ideology also changing. Richard Nixon's Southern strategy, for example, created a new conservative coalition, but it didn't create new conservative policies. Instead, Nixon tried to co-opt Democrats by using price controls to fight inflation, setting up the Environmental Protection Agency to fight pollution, and offering a healthcare reform bill to bring down the uninsured rate. Bill Clinton similarly showed Democrats how to win in the post-Reagan world, peeling off professionals and soccer moms, without really challenging the prevailing "era of big government is over," deregulating ethos.
So will 2008 be an ideological inflection point? Well, like the French Revolution, it's too early to say. Turning points come when the old policies aren't working, and the old policies don't work when there's a big monetary shock. That doesn't mean everything else is irrelevant—some policies are good ideas and others aren't—but rather that politics is a status quo business, and as long as the Fed is keeping the economy growing, people tend to be reasonably happy with what they have.
But there's something a little false about any "turning point." It's something we half-invent in retrospect. FDR's New Deal took Hoover's half-measures and made them full-measures. Reagan deregulated business like Carter had already started to. And Obama, well, he used the same healthcare plan as Mitt Romney. But if politics is the art of the possible, then these stories we tell matter because they change what we think is possible.
And that only changes when the Fed thinks something isn't.