why did the populist party support William Jennings Bryan, a democrat, for president in the presidential election of 1896?

Bryan was the only candidate who was the silver supporting candidate.

Explanation:

In the presidential election of the year 1896, where the democratic party were in support of Arthur for the vice presidential election, populist party did not like this candidate because he was a very wealthy candidate and was a business man.

The populist party was in support of William Jennings Bryan for this position because he was the only candidate fighting for that position who was supporting the silver ans was a silver supporting candidate.