Commentary on the 2012 election has featured unusually prominent (and intelligent) perspectives from political science—most notably from Brendan Nyhan and in Ezra Klein’s Washington Post blog. The political science approach has stressed the relationship between the economy and presidential outcomes, while downplaying the significance of tactical political decisions, campaign rhetoric, or other types of horse-race coverage. And, given the likely economic data for 2012, theories from political science suggest that the President’s re-election chances aren’t all that good.

In the last few weeks, we’ve seen more attempts to apply a historical lens to 2012. Virtually the only positive historical example for Obama comes from 1948, in a scenario outlined by Norman Ornstein in the New Republic.

As an Obama supporter (though, admittedly, one deeply disappointed by his administration’s hostility to due process on campus), I can see the superficial appeal of the 1948 analogy. Like Truman, Obama has been confronted by both a bitterly partisan and extremely conservative congressional opposition. (There were far more moderate and liberal in 1947 than now, but it’s worth remembering that at the start of the 80^th Congress, more than 200 Republicans requested membership in the HUAC, while the 1946 Senate freshmen class included Joe McCarthy.) Like Truman, Obama’s relationship with some key elements of the Democratic coalition (such as organized labor) seems based as much on antipathy to the GOP Congress as a common vision. Like Truman, Obama’s congressional opponents—at least based on recent polling—appear to have overreached.

But there are some pretty compelling differences between 1948 and 2012, even beyond Truman’s and Obama’s radically differing personalities. (It’s hard to imagine Obama running as a man-of-the-people populist.) The Republicans almost certainly will be more unified in 2012 than 1948, even if they nominate Mitt Romney. But perhaps most important, an Obama attack on a “do-nothing Congress” will be hard to apply just against Republicans in the House. And even though the age of filibusters has effectively transformed the Senate into a super-majoritarian institution, Democrats control the Senate.

It’s worth remembering that Truman’s 1948 victory coincided with Democratic sweeps in the House and Senate. Both chambers returned to Democratic control. Of the battle for control of the presidency, the Senate, and the House in 2012, it seems to me the safest bet, given the map, is for Republicans to take the Senate. (The Democrats’ 2010 losses in three blue states—PA, IL, and WI—were crippling in this regard.) 1948 was a broad-based Democratic victory in which Truman played a key role. Whatever the outcome, 2012 seems unlikely to be a Democratic sweep.