Final answer:
William M. Boss Tweed of Tammany Hall is most associated with supporting political corruption and fraud, primarily through graft, bribery, and rigged elections, which ultimately led to his arrest and imprisonment.
Step-by-step explanation:
The action that William M. Boss Tweed of Tammany Hall most supported was political corruption and fraud. Tammany Hall was infamous for its use of graft, bribery, and rigged elections to extort money from the city of New York during the 1860s and 1870s. Although some funds were directed towards public buildings and helped to create jobs, a significant portion of this money enriched Boss Tweed and other machine bosses through kickbacks and bribes.
Tweed's corrupt practices were eventually challenged by reformers like Samuel J. Tilden, leading to Tweed's arrest and imprisonment for his crimes against the city. Despite the machines achieving some results for their constituents, Boss Tweed's legacy is primarily characterized by the widespread corruption that underpinned his power.