Yeah, Policy Matters
Princeton economist Larry Bartels observes a trend:

The Census Bureau has tracked the economic fortunes of affluent, middle-class and poor American families for six decades. According to my analysis, these tabulations reveal a wide partisan disparity in income growth. The real incomes of middle-class families grew more than twice as fast under Democratic presidents as they did under Republican presidents. Even more remarkable, the real incomes of working-poor families (at the 20th percentile of the income distribution) grew six times as fast when Democrats held the White House. Only the incomes of affluent families were relatively impervious to partisan politics, growing robustly under Democrats and Republicans alike.

The cumulative effect of these partisan differences is enormous. If the pattern of income growth under postwar Republican presidents had matched the pattern under Democrats, incomes would be more equal now than they were in 1950 — a far cry from the contemporary reality of what some observers are calling a New Gilded Age.

It might be tempting to suppose that these partisan differences in income growth are a coincidence of timing, merely reflecting the fact that Republicans held the White House through most of the past three decades of slow, unequal growth. The partisan pattern, however, is remarkably consistent throughout the postwar period. Every Republican president since Dwight Eisenhower presided over increasing economic inequality, while only one Democrat — Jimmy Carter — did so. (I allow one year for each president’s economic policies to take effect, so the recession of 2001 is counted against Clinton, not Bush.)

Bartels also grapples with the question of why Republicans win elections at the presidential level even though their policies typically don't favor working- and middle-class households over the course of their presidencies, and concludes that the tendency of Republican presidents to produce good economic results, broadly speaking, in election years--but pretty much only election years--specifically explains their success. Maybe there's something to this; the Reagan expansion was going pretty well by 1984 after two horrible years, and 2004 was easily the best year of Bush's presidency to that point.

His explanation, that early in presidential terms, Republicans tend to inflict economic pain (through "reining in inflation and cutting social spending") while Democrats invest in stimulus "producing economic booms that raise all boats in their second and third years but trail off as the next election approaches," doesn't hold up quite as well to me. Republican presidents tend to sling the pork around--which we might describe in a less pejorative way as "stimulus"--when they're up for re-election, and the Democrats have had exactly as many incumbents defeated in a re-election bid since WWII as the Republicans: one each (Carter and Bush 41).

But that's also less important than the trend itself: when you prioritize investments in people and broad-based growth over de-distributive policies that favor those who already have the most, and view government as the art of the possible rather than a "beast" to "starve," a larger segment of the public tends to benefit.