"If the party shifts to the middle they'll lose more of the conservative vote"
Which "conservative vote" -- the vote of those who stay home and promise to vote next time, IF Republicans will do exactly as they demand, or else, but stay home at every election? Or the vote of those who are so conservatives that they get out and vote for Perot or Buchanan, handing victory to the Dems?
"Which 'conservative vote' ?"
The conservative vote which held the house for the last 12 years and elected Bush the last two times. That conservative vote...