Who was the first Democrat elected president since Buchanan in 1856?

The correct answer is Grover Cleveland, who was the first Democrat elected president since James Buchanan in 1856. Cleveland's election in 1884 marked a significant moment in American political history as it ended a long period of Republican dominance following the Civil War. This election signified a return of the Democratic Party to the presidency after nearly three decades.

Cleveland was known for his reform-oriented approach and focus on reducing tariffs, maintaining honesty in government, and opposing the extravagance of his predecessors. His presidency also tackled issues like labor strikes and the economic disparities of the Gilded Age, emphasizing the complex challenges facing the nation during this period of rapid industrialization and social change.

The other options reflect different political contexts and do not align with the time frame relevant to the question. William Howard Taft, Jimmy Carter, and Woodrow Wilson all came to power in the 20th century, long after Cleveland. Thus, Cleveland stands out as the answer that directly addresses the question regarding the first Democratic president after Buchanan.