Final answer:
The Populist Party is considered a failure due to its inability to sustain political power, failure to build a broad coalition among urban workers, and the co-opting of its platform by the major political parties after the economic recovery post-1893 and the 1896 presidential election.
Step-by-step explanation:
The Populist Party is often considered a failure by historians because, despite achieving some legislative success and impacting the national political discourse in the early 1890s, it ultimately failed to translate its platform into sustained political power. The economic recovery that began after the Panic of 1893 reduced the sense of crisis amongst farmers and workers that the Populists' platform relied on. Additionally, key Populist states like North and South Dakota, Nebraska, Colorado, and Idaho reverted to Republican and Democratic control, indicating a halt in the party's influence in the West after the Populists rejected fusion with the Democrats.
Following the support of Democratic candidate William Jennings Bryan in the 1896 presidential election and his subsequent defeat, the Populist Party's alignment with the Democrats became an issue, resulting in a loss of distinct party identity. The party struggled to appeal to the new urban electorate and reconcile the differences of the ethnically and racially diverse urban workforce with its predominantly old-stock Anglo Protestant Farmer's Alliance base. The inability to secure a significant urban presence and the absorption of Populist ideas into the agendas of the major parties further diminished the relevance of the Populist Party.