Salesforce wordpress api method campaign id

Can I add a lead into salesforce with a campaign id field using the api method? I know you can do it with the web-to-lead method. But when I use the api method, I do not see any “campaign id” field under the “map form fields to salesforce fields” section.

Am I missing something, or do we need to use web-to-lead method in order to file lead submissions under specific campaigns?

Thanks!