For generations, political operatives have revisited past presidential elections to try to predict the outcome of their present-day campaigns. History doesn’t repeat itself, but it does rhyme, as Mark Twain supposedly quipped. This year, Republicans are pointing to 1992, when a Democratic challenger won, and Democrats favor 2004, when a GOP incumbent prevailed.

In 1992, the incumbent president, George H.W. Bush, lost to Arkansas Gov. Bill Clinton. That election boiled down to “Trust vs. Change.” The voters trusted Bush much more than Clinton, who had extramarital affairs and dodged the draft. But they were hungry for the change that Clinton represented.

This time, it’s trust versus change again. Polls show that voters like and trust President Obama more than Mitt Romney. But they give the presumptive GOP nominee the edge when it comes to the economy, the No. 1 issue by far. Despite personal respect he commanded and his foreign-policy triumphs, Bush the incumbent won only 37 percent of the vote – a good sign, Republicans say, for Romney.

One big difference this year compared with 1992 is that Romney hasn’t convinced voters yet that he represents real change rather than a default position (not Obama) or, worse, a return to the failed conservative policies of the past. And an awkward Romney has already proved he’s no Bill Clinton on the stump.

There’s no billionaire Ross Perot running this time, yet little-noticed third party candidates could still determine the election, as Ralph Nader did in 2000. Former Rep. Virgil Goode, the nominee of the right-wing Constitution Party, is at 9 percent in Virginia, according to one survey. Even if he drops to 2 percent or 3 percent, Goode, who represented southern Virginia in the House for six terms, could hand that state to Obama. Gary Johnson, the Libertarian Party candidate, may siphon voters from the president in Colorado.

At Obama’s campaign headquarters in Chicago, they like the 2004 analogy: Stiff Massachusetts rich guy with lukewarm support in his own party comes up short against a sitting president despised by the opposition but buoyed by a strong get-out-the-vote effort. John Kerry, the Democratic nominee, led President George W. Bush for months in the polls. But he couldn’t recover when he got “Swift- boated” – attacked in a campaign of distortions about what was supposed to be one of his greatest strengths, his service in the Vietnam War.

Sound familiar? Kerry was outraged over those attack ads. Now Romney thinks the assaults on his years at Bain Capital Partners, which he touts as evidence of his job-creation abilities, are out of bounds. But they, too, have been effective so far.

One big difference from 2004 that might favor Romney is that Bush wasn’t running for re-election in a sagging economy. And as the president was seen as standing up to terrorists after the Sept. 11 attacks, he could hold a successful thematic convention dedicated to championing his character. Killing Osama bin Laden helps Obama on national-security issues, but that won’t give him much of a boost coming out of the Democratic National Convention in Charlotte next month.

Romney’s dream is to reproduce 1980. That year, President Jimmy Carter and former Gov. Ronald Reagan were neck and neck until the end. Then the country broke sharply for Reagan amid double-digit inflation and high interest rates. But as Ed Rollins, an adviser to Reagan’s 1980 campaign, says, Romney doesn’t hold a candle to Reagan as a candidate. And voters deserted Carter partly because of the failure of a last-minute deal to rescue the American hostages in Tehran. Memo to Republicans: Obama won’t be your Carter.

The Obama team pines for 1984, when the economy turned up enough for Reagan to proclaim that it was “morning in America,” allowing him to crush Walter Mondale, even though the unemployment rate on Election Day was 7.2 percent. The recovery this year has been too anemic for that kind.

Democrats who read history can only dream of 1936. That year, Franklin Roosevelt ran for a second term as the U.S. was beset by double-digit unemployment, though it had been significantly reduced since he was elected in 1932. Like Obama, he moved left during the campaign, saying of the wealthy, “I welcome their hatred.” His challenger, Alf Landon, campaigned hard against a new program called Social Security. Even though the benefits wouldn’t kick in for four more years (not unlike Obama’s health-care law), voters trusted Roosevelt to have their backs.

What will happen in 2012? We don’t know. One of the fun things about politics is that there are no reruns, only echoes that reverberate in our historical imaginations.