Some thoughts... please don't misconstrue this as pointless pessimism, I sincerely mean to be constructive, but two things: First, and I say this as an active musician, from a family of musicians, who's also worked in record stores for over ten years, and booked shows too... the
only well known name on that list of "bands that support Ron Paul," is Jimmy Vaughn. I know, I know... there's more than likely a slew of great bands on that list that people haven't heard of yet. I'm not making a claim as to whether the bands are good or bad, I'm just stating what I believe to be this fact: none of the bands on that list, other than J. Vaughn, will draw well, if at all, the out of town bands in particular. The cruel truth is, it doesn't matter if they're good, if no one's heard of them, who will care? I would of course, love to be proved wrong. A million people?? You'll need some seriously
major players to pull that off. I'd advise to aim ridiculously high, and then work your way down.
Second, you want to pull this off by July 14th?

No. Way. At. All. Again, I'm only trying to help here. For that level of an event, the organization needed, from top to bottom would put it somewhere in the timeframe of Spring 2008,
maybe. You'll need a legit promoter or promotion company, a first class sound reinforcement company, or in-house p.a.. If you're going to go "festival style," you might need festival permits, alcohol licenses, security, sound engineers, production mangagers, stage hands, clean up crew, outhouses, etc. etc. This is a maaaaaasssive undertaking that would also greatly benefit from a ton of sponsoring. If this is supposed to be a benefit show, you will be lucky to even make back the money you spent on setting all of this up unless you charge a crazy entrance fee, at which point, no one will want to go and the whole "benefit," will be lost. Intimidating stuff indeed.
Otherwise, as just a suggestion, what I see as a more practical alternative would be to simply have an "all day" musical event in your city. Find a decent sized venue, anything from 150 to 1000 capacity venue would be fine, and book whatever good,
solid local bands you can get to fill the bill. Any national bands/performers, put on the end as headliners. Do it on a saturday, start it around noon, give local bands no more than 45 minute sets (trust me), make it a bbq or something, have it end around midnight. Involve some other aspects like, t-shirt giveaways, Ron Paul sign making contest, pay-per-entry pie eating contest, etc.,.. I dunno, whatever you can think of. If it's at a bar/venue, try and get beer/booze vendors involved to get crazy beer deals, PBR is good for this. Again, July 14th? You'd have to start working on this yesterday, and not rest until the day of the event. It always always seems easier until you get bogged down with the details. Attention to detail is absolutely KEY. I would think something in September or October would be much much easier to manage, though it will still be a bear of a job. Plus, the further you push it back, the more time you have to promote it. Plus, most venues of this size will in all likelihood, already be booked. If the above style event still seems like a hassle, then go even smaller.
Now, if this first "smaller," event goes well. Then plan another, perhaps even bigger one sometime down the road, with bigger bands. Decent, national touring bands that are likely to draw well are most likely booked 3 to 5 months in advance, so keep that time frame in mind.
Whew! Ok, again I can't stress enough that this is all simply my take on the situation, and is in no way an attempt to discourage you. Do with it what you will.