99% of all new venture ideas tend to just not be VC fundable because the market size isn't big enough and growth rates achievable aren't high enough.
I'd start with doing a market sizing on the opportunity, and the addressable portion of it. Then try to figure out what your business model is going to look like.
Once you are done with the above (even if they are rough calculations and you only have hypotheses about your business model), the answer of whether the venture could be fundable or better bootstrapped might be apparent to you.
Happy to discuss this further with you, if you'd like to.
I have launched a few national grassroots campaigns, and have seen the tremendous growth in the quality and complexity of products that are out there. I stay on top of the new technologies to best advice clients that looking to add a grassroots piece to their current or future advocacy efforts.
I agree with Dan, except that I think it depends on two factors, first - what your app is going to cost, and second - how much is going to cost you to acquire paying customers once you have an app.
You might want to consider getting advice from people working in or around your target space to get some better perspective. POPVOX and Votility have great leadership that might be willing talk to you if you aren't direct competitors.
If you are in DC, 1776 has a great educational events and staff from the start-up community that would probably be willing to talk to you as well.
I am happy to follow-up on any or all of this. Good luck!