The high water mark for the establishment was probably 2000, when George W. Bush had too much Christian right support for a viable conservative challenger to even emerge. His main rival, John McCain, was running to Bush’s left.
Since 1988, conservatives have not only split their votes. They have usually shunned the conservative with the organization and finances to compete with the establishment on something like even terms in favor of candidates who would struggle to go the distance. Think Pat Robertson over Jack Kemp, Pat Buchanan over Phil Gramm, Mike Huckabee over Fred Thompson (and Mitt Romney!), and Rick Santorum over Rick Perry.
But the establishment’s grip has slowly been loosening. Buchanan beat Bob Dole in New Hampshire in 1996 and came within an Alan Keyes of defeating him in Iowa.
After the Dubya interregnum, Rudy Giuliani imploded and McCain’s campaign nearly went broke in 2007. The Arizona senator was able to right the ship, but he ended up winning fewer votes than Huckabee, Romney, and Ron Paul combined.