I'm not so sure that's true.
NYC and LA are about the same politically. Throw in the San Francisco/Oakland/San Jose area. It's the same too. Not sure where Chicago stands but I'd assume it's closer to NYC than it is Phoenix in terms of politics. So basically the top 4 biggest cities/areas are all the same. It makes it really tough to overcome.
Look at this graph. Only like 10% of the cities are conservative, and they are all on the very small end population wise.
Big cities in the U.S. tend toward the liberal side of the political spectrum, even when they're within conservative states (residents of Austin sometimes
www.pewresearch.org
I'm not even a conservative but there has to be some balance or you get the wackadoo left running amok. If it were completely slanted right you'd get the same wackadoo right policies. I don't know what the answer is but I do know letting NYC, LA and San Fran run the country is not a good idea.