Colorado’s March 3 presidential primary has attracted lengthy lists of candidates for both major parties, including all leading Democratic contenders and several challengers to President Donald Trump. RELATED: Get ready, Colorado: The 2020 Democratic presidential primary will soon be in your face To make the primary ballots, candidates could file petitions with 5,000 signatures from voters or, more commonly, simply pay a $500 filing fee with a notarized statement of intent.