Clinton tackled health care, tax increases on the rich, the North American Free Trade Agreement and welfare revisions in his first term.
Bush sharply cut taxes, twice, as the budget surplus was changing to a deficit. Obama led a brutally partisan fight for the health care overhaul now before the Supreme Court.
Will Obama boldly push for big changes in immigration, Social Security or other difficult issues if he wins a second term?
Recent history offers few hints. The last four presidents to win re-election saw their second terms bog down in scandals or controversies: Richard Nixon and Watergate; Ronald Reagan and Iran-Contra; Clinton and intern Monica Lewinsky; Bush and Hurricane Katrina and the increasingly unpopular Iraq war.
Nothing illustrates the dilemma facing a fourth-year president better than Bush's handling of Social Security.
After narrowly defeating Kerry in 2004, Bush announced: "I earned capital in the campaign, political capital, and now I intend to spend it."
In his autobiography, "Decision Points," Bush wrote, "For someone looking to take on big issues, it didn't' get much bigger than reforming Social Security." He said he "embarked on a series of trips to raise awareness about Social Security's problems and rally the American people to insist on change."
Such a call to arms, of course, often takes place in an election campaign, not after it. Bush's bid to allow partial privatization of Social Security for younger workers quickly collapsed in the face of strong Democratic opposition and tepid GOP support.
"I may have misread the electoral mandate by pushing for an issue on which there had been little bipartisan agreement in the first place," Bush wrote. "The failure of Social Security reform shows the limits of the president's power."
Obama may have "more flexibility" to deal with missile defense, immigration and other issues if he wins a second term. Whether he will have a mandate to do so is another question.
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