Hilzoy wonders why more people think Barack Obama will raise their taxes than think John McCain will, despite fancy graphs indicating that neither will raise most peoples’ taxes. Three broad hypotheses spring to mind:

1. Voters do not believe Democrats (and Obama in particular) are credible on promising tax cuts or holding the line on taxes. Obama’s vote for a budget resolution that contemplated raising taxes (even if, in of itself, it did not raise them) does not help his credibility on this score. The inscrutability of how Washington works to the average voter strikes again—a similar procedural-versus-substantive vote issue, after all, was the basis for John Kerry’s “for it before he was against it” problem.
2. Voters do not believe that the promises on the campaign trail regarding taxes reflect the situation that both candidates will face after the election. Presidents do not decide fiscal policy in a vacuum; instead, both will face a left-of-center Congress committed to both the appearance of fiscal responsibility and more progressive tax rates. For example, a “solidarity” tax increase on a greater portion of the “middle class” than anticipated by Obama (however “middle class” is defined) to fund programs like universal health care is not unlikely.
3. It’s all heuristics. Voters have no actual knowledge of either candidates’ tax plans (rationally or irrationally—I’d argue rationally, due in part to point 2) and are relying on a schematic conception of politics in which Democrats are seen as more likely to raise taxes than Republicans.

Notice in the full report of the poll results the graph labeled “Economic Groups Perceived to Benefit Most in an Obama or McCain Presidency,” in which the heuristic perceptions of the public comport to a greater degree to the promised tax plans, in large part because both candidates are promising plans that—in their effects on various subsets of the population—are more consistent with what we’d expect Republican and Democratic fiscal policies to emphasize.

Incidentally, none of these explanations require voters to even be aware of the campaign spin regarding Obama’s tax positions; one suspects most voters aren’t.