In 2008, when Barack Obama was running for president, he began a minor furor by saying that “Ronald Reagan changed the trajectory of America in a way that Richard Nixon did not and in a way that Bill Clinton did not. He put us on a fundamentally different path.” The implication was that Obama wanted to put the nation on a fundamentally different path, too. And, in the context of a Democratic primary, that was taken to mean a more liberal path.

But in a recent analysis, political scientist Keith Poole applied his model for measuring politicians’ ideologies to Obama and Clinton and found Obama to be the more moderate one, at least judging by the coalitions of lawmakers who supported his initiatives.

Every model has its limits. But Poole’s effort raises an interesting question: Can we really compare the ideologies of presidents? Or does the surrounding context change so much that such studies are useless?

Consider their economic policies. Among Clinton’s first major fights in office was the 1993 budget, which raised taxes on the rich, on corporations and on fuel. The measure passed with no Republican votes. Obama, in contrast, cut taxes during his first two years in office and has called for extending most George W. Bush-era tax cuts. So in a simple analysis in which higher taxes are coded as liberalism, Clinton was clearly more liberal. In fact, Obama’s preferences more closely mirror Bush’s tax policy than Clinton’s.

Clinton’s health-care policy was, similarly, much more liberal than Obama’s. The simplest way to establish this is to note that Obama’s policy is almost a carbon copy of the Health Equity and Access Reform Today Act of 1993, which was one of the leading Republican alternatives to Clinton’s proposal.

But Obama’s place in the party is very different from Clinton’s. Obama comes from what I’d call the pragmatic-liberal wing. Clinton was a reformer. Before he ran for the presidency, Clinton’s political project was to pull the Democratic Party to the center. Nothing in Obama’s history is comparable to Clinton’s chairing of the Democratic Leadership Council. Nor is anything comparable to Clinton’s passing of welfare reform, although perhaps there would have been if House Speaker John A. Boehner (R-Ohio) had been able to reach an agreement with the White House in August.

That suggests that perhaps this is a flawed question. We’re talking about presidents when we should be talking about parties and conditions. After all, what most presidents want is to get something done in a system that is incredibly resistant to doing anything. In that context, what they get done has a lot more to do with the opportunities available to them than their personal preferences.

It’s possible that Clinton’s instincts were more moderate, but his early economic problem — high interest rates driven, in part, by high deficits — suggested tax increases in a way that Obama’s early economic problems — a decrease in aggregate demand driven by a financial crisis — didn’t. As such, Clinton’s tax increases and Obama’s tax cuts tell us more about the economies the two men faced than the ideologies to which they hewed.

The relevant institutions also have changed over the past two decades. Clinton tried to free gays to serve openly in the military and ended up retreating to “don’t ask, don’t tell.” Obama’s Democratic Party — not to mention his military — supported his effort to do away with that legislation. The difference in outcomes there tells us more about changes in American culture than personal levels of tolerance.

It’s also worth noting that Obama’s strategic choices have been shaped by the lessons and results of Clinton’s strategic choices. If Clinton’s health-care bill had passed, Obama wouldn’t have had to deal with health-care reform. If Clinton had never tried to pass such reform, Obama might have gone with a more ambitious approach, as it wouldn’t have become conventional wisdom in Democratic policy circles that Clinton’s plan collapsed in part because it tried to do too much. So evaluating them independently is more or less impossible.

I would say that Clinton was the more moderate of the two, at least compared with his party at the time. But I would also say that the difference is meaningless. Both Clinton and Obama are pragmatists who are willing to make a wide variety of ideological compromises to get things done. The composition of Congress, the state of the economy and the institutions they lead have much more say in the shape of their presidencies than the marginal differences between their personal policy preferences.

Which is, perhaps, a warning to future presidents who hope to be transformational. It’s not always up to them.

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