Republican candidates habitually genuflect to the memory of Ronald Reagan, and this year the candidate who emerges as the nominee for president will be hoping to emulate one Reagan accomplishment in particular: evicting a one-term Democratic incumbent who struggled during tough times.

President Obama is vulnerable this year, according to the conventional wisdom, because of the lingering effects of the Great Recession, including a persistently high rate of unemployment. In this scenario, Obama would be playing the part of President Jimmy Carter, facing a challenge most likely from Mitt Romney as the would-be Reagan.

As we scan the decades since the Second World War, the 1970s and the 2000s stand out as the most difficult and troubled. It was during the 1970s that the post-war era of booming prosperity faltered because of recession and inflation rates in the double digits. The period brought us the oil crisis, with the formation of OPEC and the oil embargo that produced lines of cars at gas stations. The nation struggled through the humiliating end of the Vietnam War and the crimes and misdemeanors of Richard Nixon, as well as the deterioration of the cities and spiraling crime rates.

Further, President Carter had to contend with events overseas that were resistant to American influence, notably the Iranian revolution and the hostage crisis that ended only on the day that Ronald Reagan was inaugurated.

The 2000s were ushered in by the attacks of Sept. 11 and unfolded in the shadow of wars in Iraq and Afghanistan and the lingering fear of terrorism. The nation had to live through the crimes and misdemeanors of the Bush administration, all of it capped with the most significant economic collapse since the Great Depression.

Despite these similarities, these two troubled decades have played out differently, and with less than a year before the 2012 election, Obama would seem to be in a stronger position that Carter was.

Carter came into office in 1977 promising to bring honesty and integrity to politics. And yet he never managed to surmount the challenges of the time — including high inflation and the crisis in Tehran. He sent a team by helicopter to rescue the American hostages, but the mission was scuttled after a crash in the desert. His efforts to free the United States from foreign oil floundered.

Carter took office in the middle of a long period of conflict and change, and it did not seem as if he effected any great improvements. By contrast, Obama took office in the midst of a specific economic calamity that had begun on the watch of his predecessor. He has struggled with an obstructionist Congress, but he has not floundered. He took action that staved off disaster. It is not an easy the case to make that things would have been much worse, but the case can be made. Obama can point to the prosperity of the U.S. auto industry and to the tens of thousands of jobs that exist as a result of the auto bailout, reminding voters that Republicans all too often were willing to let the auto industry, and all its chain of suppliers, crumble into bankruptcy.

Overseas, Obama has not been a prisoner of events as Carter was. His secret mission did not crash in the desert. It slipped into Pakistan and killed Public Enemy Number One — Osama bin Laden. Obama’s careful and shrewd foreign policy has fostered change in places like Libya without the bravado and foolishness that in the past have mired us in faraway conflicts.

Carter was unlucky. Obama has always seemed to be the luckiest of presidents.

Many people are still suffering because of the poor economy, and we are struggling through a difficult time. Obama’s policies can be faulted on a variety of grounds, but he has been taken on events and issues in a big way — health care, economic stimulus, financial regulation. These are successes the like of which Carter did not achieve.

That doesn’t mean that Romney, should he win the nomination, won’t mount a fierce case against Obama and put the president to a stern test. But those who remember know that Obama is no Jimmy Carter.