That's not true at all. I was an active establishment Republican and I saw first hand how the far right wing of the party co-opted the party.
When estabishment, pro-business and center right moderates are willing to fight as hard and as long and willing to shout down opposition for as long as it takes to get their way, then the Republican party will migrate back towards the center and political compromise.
Say what you want to about the right wing socially conservative base of the party. They may only represent a minority of Republicans but they are the most motivated activist in American politics.
Eventually the other coalitions of the Repulbican party will have to fight fire with fire to prevent their party from becoming a permanent minority. The decline at the national level is obvious and it's begining to manifest it'self at the State level.