I don't believe that the people who cite Reagan's 11th Commandment - to not speak ill of a fellow Republican - know its origin or the context in which it was used.
First, it didn't start with Reagan. California Republican Party chair Gaylord Parkinson started it to prevent liberal Republicans from attacking Reagan for his conservatism.
Got that? It was to keep the moderates from calling conservatives extremists, and this was before Reagan's run for the presidency.
On the campaign trail, Reagan himself didn't abide by it.
For example, during the North Carolina swing in his bid for the White House in 1976, Reagan accused Ford of presiding over the decline of our military. "Mr. Ford and Dr. Kissinger ask us to trust their leadership. Well, I find that more and more difficult to do." He asserted that Ford had "neither the vision nor the leadership necessary to halt and reverse the diplomatic and military decline of the United States."
Did he speak ill of Ford? He sure did. He accused Ford of essentially being a moderate.
So the next time someone asserts that you can't criticize another Republican because of Reagan's 11th Commandment, remember that they're likely the ones who are quickest to criticize people like Ted Cruz who are actually fighting.
Every politician regardless of political stripe is worthy of criticism when they ignore the people and strengthen the hand of an already too powerful government. The 11th Commandment didn't begin to protect all Republicans. It got its start to protect conservatives from moderates.
Chew on that.