“There are days when I say that one term is enough,” President Barack Obama said in June. His prospective opponents certainly feel that way, and if Obama studied recent presidencies, he might find good reason beyond his current woes for packing it in.

More often than not, second terms — often painfully achieved — have been very difficult, with presidents beset by scandal and political environments that kept them from achieving their goals.

Two recent presidents, Richard Nixon and Bill Clinton, faced impeachment in second terms. Two others, Lyndon B. Johnson and George W. Bush, became mired in wars that sapped their political and public support. Ronald Reagan had to surmount a high-level scandal that cost him top advisors.

Of course, Obama may not win re-election next year. Continued low economic growth, high unemployment and a toxic partisan atmosphere voters disdain could make him the fourth president in 36 years to be rejected at the polls.

Still, polls show voters split on whether Obama deserves a second term, and his reasons for seeking one is similar to that of many predecessors. As he told NBC’s Ann Curry in that same interview, “What keeps me going is a belief that the work that we started in 2009 is not yet complete.”

Indeed, with Republicans poised to add Senate control to their House majority next year, Obama could find it hard to undertake many new initiatives in a second four years, barring a renewal of the kind of bipartisanship that seems a distant memory.

That was how both Republican Reagan and Democrat Clinton achieved significant second-term successes in economic policy. Reagan worked with congressional leaders of both parties to enact a major measure that spurred economic growth by simplifying the nation’s complex tax laws. Clinton joined the GOP in passing a tax-cut bill that helped produce a balanced budget.

Those successes help explain why they left office with job approvals in the 60s, higher than those of other recent chief executives. Reagan and Clinton remain presidential role models for their respective parties.

In general, though, the modern second-term record is pretty dismal.

Republican Dwight Eisenhower, easily re-elected in 1956, presided over a severe economic recession that helped Democrats win the next election.

Johnson, winning a full term as John F. Kennedy’s successor, enacted a series of landmark domestic measures before the Vietnam War consumed his presidency and led to his retirement and replacement by Republican Nixon.

Nixon, after carrying all but one state in his 1972 re-election, was forced to resign in the face of almost certain impeachment and conviction for covering up the Watergate scandal.

Reagan’s second term was clouded by a scandal in which he misled Congress by selling arms to Iran and illegally using the funds for a war against Central American leftist insurgents. Yet, he not only achieved tax reform but a major arms reduction treaty with the Soviet Union.

Clinton actually was impeached by a Republican-controlled House for lying under oath about his illicit White House affair with an intern. But the Senate refused to convict him and the economy continued a lengthy boom.

Bush, already mired in the war he started against Iraq, saw the economy collapse into the recession that persists today.

A re-elected Obama presumably would still struggle to bolster the nation’s long-term economic well-being, probably with the kind of additional measures to reduce the budget deficit and spur growth he plans to seek next month.

While new initiatives might be difficult, a second term might enable him to ensure the long-term future of his top domestic achievement, the controversial health care reform law, and finish extricating the U.S. from wars he inherited in Iraq and Afghanistan.

After all, two terms make it harder than one for future presidents to undo a predecessor’s achievements.