It is difficult to overcome but it is not "invincible". When the republicans take conservative stands it is much easier. When they take progressive stands such as amnesty for illegals and support for homosexuals, it makes things so much more difficult.
I have been fortunate to have found a few converts over the years, but lately all I hear is that there is not a dime's worth of difference between republicans and democrats so there is no incentive for anyone to switch.
If the republicans choose any of the liberal presidential candidates like Rudy Mc Romney, it will be even more difficult.
Good point.