His great 'sin' is actually a bunch of sins, and those sins happen to be his liberal positions on lots of issues.
Simply put, he would split the Republican Party in half should he win the nomination.
Some of our brethren don't want to win.
If we have to win by nominating a Republican liberal, then what have we won?
No, Rudy wouldn't split the party. You would.
Don't blame him for what you're doing.