Senator Ted Cruz (R., Texas) may be the brightest light to adorn the Republican party in many years. He knows how to make the case for conservative ideas, pointing, for example, to the contrasting fates of Detroit and Houston to illustrate the superiority of conservative policies. So it’s particularly galling to see that rather than train his fire at Obama and the liberal machine that cocoons him, Cruz has become a one-man wrecking ball against Republicans. His most recent foray into sabotaging his colleagues concerned the debt-limit increase. Because Speaker Boehner sent over a “clean” debt-limit bill, Republican senators had...