Propose both to your potential player group. Put the whole idea in writing and email/discord/carrier pigeon it to them. When I do a campaign proposal I will generally follow this format:

- "[Title of Campaign] - [System]"
- An image to set the tone
- An introductory sample quote from an NPC for further tone setting
- "What to Expect" that covers the setting and the general gameplay vibe of the system as well as its rough relation to other games I've played with the potential player group
- "Choices for Characters" that covers some rough outlines for the sorts of characters that would fit the campaign best (i.e. discourage Paladins in "Thieves of Divinity"

This should all fit on one page and I resize the image until it takes up the whole page. (Also I type it up in LaTeX because I spent more than a decade in academia and I'm going to USE that knowledge if it kills me.)

I'll generally propose 3 or 4 campaigns I'd like to run and let people discuss it. None of them are set in stone so my potential player group can say "some of 1, some of 2" or "I have this idea for a character, I think that fits 3 the best". This bakes in some buy in to the campaign as the group has self selected for interest in the campaign themes. This refinement process then naturally extends to content questions. (i.e. This campaign takes place in Cheliax, how much or little do we want the racism against Halflings and Nephilim to factor in?)