It is known that the US economy has grown faster during Democrat presidencies, but the Democrat-Republican presidential GDP growth gap cannot be attributed fully to policy differences, nor did Democrat presidents happen to benefit systematically from more favorable external shocks. The question why thus remains open. We postulate that, if the effect is real, a Democratic Party performance advantage should be present with respect to measures of political control other than just the presidency. We investigate partisan control of US state governments and show that national GDP grew faster when more states had Democrat governors and Democrat-majority state legislatures: a one-standard-deviation increase in the share of governorships controlled by the Democratic Party (unified Democrat state governments) is associated with a 0.57-percentage-point (0.77-percentage-point) increase in the real US national GDP growth rate. The effect appears to occur on top of the presidential D-R growth gap, suggesting that the Democrat growth advantage may be a more generalized phenomenon. To investigate whether the effects are explained by state-level policy differences, we adopt an encompassing measure of a state’s policy priorities—state policy liberalism (in the modern, popular sense rather than the classical sense). Nevertheless, our findings are not explained by state policy liberalism. That result echoes the puzzle at the national level that key national policy differences cannot account for the presidential growth gap.

众所周知，民主党总统任期内美国经济增长较快，但民主党与共和党总统之间的GDP增长差距不能完全归因于政策差异，民主党总统也没有碰巧从更有利的外部冲击中系统性地受益。为什么这样的问题仍然悬而未决。我们假设，如果效果是真实的，民主党在政治控制措施方面应该存在表现优势，而不仅仅是总统职位。我们调查了美国各州政府的党派控制，并表明当更多州拥有民主党州长和民主党占多数的州立法机构时，国家 GDP 增长更快：民主党控制的州长比例增加一个标准差（统一的民主党州政府） ) 与 0.57 个百分点 (0. 77 个百分点）美国实际国内生产总值增长率的增加。效果出现在总统 DR 增长差距之上，表明民主党的增长优势可能是一个更普遍的现象。为了调查这些影响是否由州一级的政策差异来解释，我们采用了一个国家政策优先级的综合衡量标准——国家政策自由主义（现代的、流行的而非古典的意义）。然而，我们的发现并不能用国家政策自由主义来解释。这一结果与国家层面的难题相呼应，即关键的国家政策差异无法解释总统增长差距。