What did the Democratic Party do to prevent the populists from gaining too much power

They appealed to peoples racism.

Explanation:

Populism started to arise around the 1880s and many African Americans joined them, especially the Populist Party. This party was a major political threat to the Democratic Party in the South. If the poor white joined the African Americans the Democratic Party would not have more chance against the Populists.

With that, the Democratic leaders appealed to racism, making it harder for African Americans to vote and appealing to people's racism so they would not join forces.

They appealed to peoples racism.