Andrew Gelman elaborates on the conditions that make U.S. presidential elections pretty predictable, but that don’t let us say the same thing about other kinds of elections:
(a) A long history: we can predict this year’s election, to some extent, from last year’s. The U.S. isn’t a country like Guatemala where they’ve only been having competitive elections for a few years.
(b) Clear separation between the parties. Talk about Tweedledee and Tweedledum aside, the Democrats and Republicans are, according to Huber and Stanig, further apart on economic issues than are left and right groupings in just about every other industrialized country.
(c) Only two major candidates. Anderson in 1980, Perot in 1992 and 1996: they cane close but they didn’t quite make it a real three-candidate race. It basically worked to focus on the Democrat and the Republican.
(d) Equal resources. Not quite: Nixon reputedly massively outspent McGovern in 1992, Bush had the edge over Gore in 2000, and Obama had a few hundred million to spare in 2008. Still, compared to referenda and elections for congress and governor, presidential races are on a pretty level playing field.
(e) A clear schedule: Voters have many months to sort out the information and make up their minds.
This is worth keeping in mind when you hear the intuitively wrong-sounding empirical results on the lack of campaign effects. What the political science is telling you isn’t that presidential election campaigns couldn’t make a difference to election outcomes, it’s telling you that they don’t seem to make a difference in practice. But if one candidate just refused to fundraise, or did fundraise but did something wildly eccentric with the money, then for all we know that might make a big difference. You could imagine a candidate deliberately trying to tank the race, or just acting plain-out weird. What if John McCain delivered lengthy speeches denouncing his own policy agenda? But in practice we always see two well-funded, well-known candidates run pretty conventional campaigns and within that context the ups-and-downs of the campaign trail don’t seem to make a difference.