After the 2018 election, it took nearly a month for the winner to be determined in the Central Valley congressional race between T.J. Cox, the Democrat, and David Valadao, the incumbent Republican. Mr. Valadao eventually conceded.

This time, California — like the other 13 states, American Samoa and Democrats Abroad that voted on Tuesday — will have to figure out which candidates won enough votes to cross the 15 percent threshold to accrue delegates. And California will have to do those calculations both statewide and in each of its 53 congressional districts.

Of California’s 415 delegates, 144 will be allocated according to the statewide results — so whichever candidates win at least 15 percent of the vote will get a share of those delegates. The remaining 271 delegates will be divided among the congressional districts.

The more Democratic a congressional district is, the more delegates it has. California’s 12th and 13th districts — in San Francisco and Oakland — have seven delegates each, while the rest of the districts have four, five or six.