WASHINGTON — Now that President Obama has overcome Mitt Romney, “super PACs” and a sluggish economy, he faces a challenge with deep roots in political history: what historians and commentators call the “second-term curse.”

It is almost a truism that second terms are less successful than first terms, especially domestically. Franklin Delano Roosevelt lost his hold on Congress with his 1937 plan to pack the Supreme Court. Ronald Reagan faced the 1986Iran-contra scandal. Bill Clinton was impeached in 1998.Richard Nixon resigned to avoid that fate in 1974.

Even George Washington had angry mobs surrounding his house in Philadelphia to denounce him for the Jay Treaty with Britain dealing with the aftermath of the Revolutionary War; they wanted him to side with France.

But despite these and other failures, most second-term presidents also have accomplishments to be proud of, though perhaps shadowed by a tinge of failure.

Stephen Hess, a scholar at the Brookings Institution and a veteran of the Eisenhower, Nixon, Ford and Carter administrations, said there were several explanations for the second-term curse.

One is that presidents try to push their best ideas when they first take office, often leaving them, he said, without “a whole new set of ideas” for the second.

Presidents also select the best members of the White House staff or cabinet when they first take office. When the pressure cooker of Washington or better jobs lead those first choices away, their successors are often not their equals.

Roosevelt may have had the most accursed second term. The biographer Jean Edward Smith called it “a disaster.” After the 1936 death of Louis Howe, his closest adviser for years, he had no one to tell him what a bad idea the court-packing scheme was. It split his party. Conservative Democrats deserted him and allied with Republicans to deny him almost all domestic legislation.

And while that hurt Roosevelt politically — Mr. Smith said he “shot himself in the foot” — he followed with an even worse decision, cutting federal spending in the belief that the Depression was conquered. That brought on a deep recession. With that decision, Mr. Smith wrote, Roosevelt “shot the country in the foot.”

Overwhelming victory can often lead to second-term hubris, persuading a president that the country thinks he can do no wrong. As Lou Cannon, the Reagan biographer and Washington Post White House reporter, observed: “Landslides are dangerous to the victor.” Roosevelt lost only two states in 1936; Nixon lost only Massachusetts and the District of Columbia in 1972.

Reagan lost only one state in 1984, and the next two years were “the least successful of Reagan’s 16 years in office,” including his years as governor of California, Mr. Cannon said. Even a narrow victory can create overconfidence. In 2004, George W. Bush won 50.7 percent of the vote, which was no landslide (even compared with his 48.3 percent share four years earlier). But he treated the victory as a huge mandate, and plunged ahead with a plan to privatizeSocial Security in 2005, as he had promised during his re-election campaign.

But the Social Security plan went nowhere. Republicans cringed, and Democrats eagerly united in opposition.

Second-term presidents are also lame ducks, parrying ambitious would-be successors in the opposition and in their own party. Dwight Eisenhower often complained of the recently enacted 22nd Amendment, limiting presidents to two terms. But earlier presidents faced the same problem, because tradition back to George Washington had established the same term limit, until Roosevelt ran for his third term.

But are second terms inevitably cursed?.......MOREMOREMORE