I develop a dynamic political economy theory of optimal taxation and budget distortions in a model with partisan politics. Under asymmetric information, politics affects the distribution of utilities in the economy. Political regime switching introduces fluctuations of this distribution. These fluctuations justify strategic budget distortions by governments currently holding office and willing to favour their redistributive concerns against future majority. Under quite general assumptions on preferences, these distortions take the form of budget deficits (resp. surpluses) with leftist (rightist) governments. Endogenizing the probabilities of getting elected may reverse this result. This paper presents a dynamic political economy theory of taxation policy showing how partisan governments create strategic budget distortions. Under quite general assumptions on preferences for redistribution, these distortions take the form of budget surpluses (resp. deficits) when rightist (resp. leftist) governments hold office. Being uncertain on whether it will remain in office in the future, the current government chooses a level of deficit which will favour its redistributive concerns against those of future majorities. It does so by constraining the redistributive policy of its successor through the budget constraint that the latter inherits. A leftist (resp. rightist) government is more (resp. less) enclined to redistribute income. By running some deficit today, the leftist government ensures that society gets poorer tomorrow. A future rightist government will redistribute more as society gets poorer. The implemented tax policy will thus be close to what a leftist government would have chosen itself. On the contrary, by running a surplus today, a rightest government relaxes the burden of taxation imposed by tomorrow's leftist government on high income agents. This leftist government will be less eager to redistribute and will adopt the rightist party's behaviour. Under political regime switching, strategic distortions of the State budget constraint become important tools for current governments willing to favour their own redistributive concerns against those of future majorities. As a result of this dynamic game between partisan governments playing at different points in time with the State budget constraint, future policies blend together the preferences for redistribution of current and past governments. The commitment value of budget deficits has already been stressed by Persson and