In 1932, platform debates were aired nationwide and reported in newpapers everywhere. Here are the Democratic, Republican, Prohibition and Liberal Party planks on legalization of alcoholic beverages:
Prohibition party plank: [Invokes Almighty God and the Prince of Peace…] We unequivocally oppose the repeal or weakening of the Eighteenth Amendment or of the laws enacted thereunder, and insist upon the strengthening of those laws. …can and will coordinate all the powers of government, Federal, State and local, strictly to enforce, by adequate and unescapable punishment of all violators, this wise and beneficent law. (…) We indict and condemn the Republican and Democratic parties for the continued nullification of the Eighteenth Amendment and their present determination to repeal the amendment on the excuse that it cannot be enforced… (Johnson and Porter 1975 337-338)
Republican prohibition plank: We do not favor a submission limited to the issue of retention or repeal, for the American nation never in its history has gone backward, and in this case the progress which has been thus far made must be preserved, while the evils must be eliminated.
We therefore believe that the people should have an opportunity to pass upon a proposed amendment the provision of which, while retaining in the Federal Government power to preserve the gains already made in dealing with the evils inherent in the liquor traffic, shall allow the States to deal with the problem as their citizens may determine, but subject always to the power of the Federal Government to protect those States where prohibition may exist and safeguard our citizens everywhere from the return of the saloon and attendant abuses.
Such an amendment should be promptly submitted to the States by Congress, to be acted upon by State conventions called for that sole purpose in accordance with the provisions of Article V of the Constitution and adequately safeguarded so as to be truly representative. (Johnson and Porter 1975 348-349)
Liberal Party prohibition plank: We demand the immediate repeal of the Eighteenth Amendment. We demand that, without modification or compromise of any kind, the entire question of liquor control shall be returned to the States, where the use of beverages can be regulated by local option in each State, county, city, or otherwise, or prohibited, according to the wishes of the people therein. With this local option, or other control established, the sale of beverages, except that saloons are permanently abolished, should be freely permitted by law. (…)
To those who say that the system should be modified so as to permit the sale of wine and beer, we answer that you cannot modify anything that is essentially wrong. You have not thought the matter through. Besides, any modification of any kind would fail to correct the central evil. The bootlegger would still rule the situation, and the traffic in hard liquors, now so universally effective, would still make it necessary to preserve the whole system of futile enforcement, together with the violence and corruption which now disgrace it. Therefore, the Eighteenth Amendment must go out of the Constitution, root and branch. (The Liberal Party in America, 1931 pp 106-7)
Democratic prohibition repeal plank: We advocate the repeal of the Eighteenth Amendment. To effect such repeal we demand that Congress immediately propose a Constitutional Amendment to truly represent the conventions in the states to act solely on that proposal; we urge the enactment of such measures by the several States as will actually promote temperance, effectively prevent the return of the saloon, and bring the liquor traffic into the open under complete supervision and control by the states.
We demand that the Federal Government effectively exercise its power to enable the states to protect themselves against importation of intoxicating liquors in violation of their laws.
Pending repeal, we favor immediate modification of the Volstead Act; to legalize the manufacture and sale of beer and other beverages of such alcoholic content as is permissible under the Constitution and to provide therefrom a proper and needed revenue.
We condemn the improper and excessive use of money in political activities. (Johnson and Porter 1975 332)
Observe that the Republicans copied the Prohibition Party platform (in 1928) and the Democrats copied the 1931 Liberal Party wet plank (calling for repeal of the Prohibition amendment). In both cases, small parties casting less than 1.4% of the vote caused the major parties to adopt or reject important changes in the laws. This is the spoiler vote leverage effect.