Even those who have tried to develop measures are cautious about generalizing. In their book, "Addressing the State of the Union," University of Northern Iowa professor Donna Hoffman and Dominican University of California assistant professor Alison Howard use one such tool: calculating how many legislative requests presidents make of Congress – and how many get adopted in the next session.
Critics often deride State of the Union messages – "empty rhetoric," some said after last year's. In fact, modern presidents include specific calls for congressional action – the median is about 31, according to Ms. Hoffman and Ms. Howard, ranging from Carter's 1979 low of nine to Clinton's 2000 high of 87.
On the surface, the numbers might seem to substantiate the difficulties of a second term. Hoffman and Howard's research shows 43 percent of the requests are passed in some form – 51 percent in a first term and only 38.6 percent in the second.
But the issue is more complicated than that, especially when considering early presidents. The nation's early leaders weren't much concerned with legislative requests. Not until Woodrow Wilson did the notion emerge of presidents as what Hoffman calls "legislators in chief."
"When measuring success, I'm not concerned about whether Jefferson got Congress to do what he wanted," she says. "[To him] it would have been anathema."
Greenberg agrees. The intense focus on 1600 Pennsylvania Avenue is relatively recent. "If you were a reporter in the 19th century, you didn't go over to the White House," he says. "You went to the Senate gallery."
Focusing too closely on what chief executives get through Congress can lead to misconceptions about modern presidents, too. Legislation is only one of their tools. Others include federal agencies, executive orders, appointments, and judicial nominations. Hoffman and Greenberg cite both Reagan and Clinton as success stories.