History tends to make Democrats nervous about the 2016 White House election. They know that since 1951 and the ratification of the 22nd Amendment to the U.S. Constitution – which limits a president to just two four-year terms – there have been seven elections in which the party that has held the presidency for eight consecutive years has sought another term.

They also know that six of those seven times, the candidate seeking to make it 12 years in a row for his party has lost. (The lone exception was in 1988, when George H.W. Bush might be said to have won President Ronald Reagan’s third term.) The 2016 Democratic standard-bearer will be fighting both history and the Republicans.

But a closer look at the record makes a strong case that there is no historical iron rule against third terms. For example, after eight Republican years beginning in 1968 – during which both the president and vice president, Richard M. Nixon and Spiro Agnew, were forced to resign their offices to avoid certain removal by Congress and criminal prosecution – Gerald R. Ford, the only U.S. president never to have been elected to national office, best-known for his then-broadly-unpopular pardon of Nixon, came within a whisker of winning a third straight Republican term.

In fact, a switch of just 5,559 votes in Ohio and 7,233 in Mississippi and Ford would have defeated Democrat Jimmy Carter.

Earlier, Nixon – seeking to follow popular President Dwight Eisenhower’s eight years – had come within 118,000 votes of winning the 1960 popular vote against John F. Kennedy, and in 2000, if Democrat Al Gore could have changed the minds of only 3,606 New Hampshire voters, he would have won the Granite State’s four electoral votes and the presidency outright, bringing a third Democratic term after Bill Clinton’s eight years, without any Florida recount or Supreme Court case.

Of course, the quality of the candidates and the campaigns they run do matter in the outcome of every national election.

But two other factors – whether voters are satisfied or dissatisfied with the way things are going in the country at the time of the election and voters’ approval or disapproval of the incumbent president – can boost or doom the nominee of the incumbent party.

Consider the all-but-impossible uphill struggle of Republican nominee John McCain in 2008. Just two weeks before Election Day, in the Gallup Poll, a mere 7 percent of Americans said they were satisfied with the direction of the country, whereas a whopping 91 percent were dissatisfied. At the same time, the Republican McCain was running to succeed, President George W. Bush, had a favorable job rating of just 24 percent.

Given such a toxic environment, the McCain campaign did not feature any posters or billboards urging “4 More Years.” By contrast, when George H.W. Bush did win a “third term,” he was helped enormously by Reagan’s 54 percent favorable rating and the electorate’s 60 percent satisfaction with the direction of the country.

Democrats cannot be encouraged by the most recent Wall Street Journal-NBC News national survey, in which Democratic pollster Peter D. Hart finds that some “73 percent of Americans want the next president to take a different approach from” President Barack Obama’s, adding, “That’s identical to late 2007, when 73 percent favored taking a different approach from” George W. Bush’s. If President Obama’s job rating is below 40 percent next Halloween, the Democratic nominee, in order to win, will need to establish her/his independence from Obama without looking disloyal to him – a difficult balancing act.

More than any third-term precedents, keep your eye next autumn on how voters feel about whether the U.S. is headed in the right direction and how they rate the job the president is doing. Those things matter more.

Editor’s note: To find out more about Mark Shields and read his past columns, visit the Creators Syndicate website at www.creators.com.