People think I’m over the top by calling Marjorie Taylor Greene the “shadow speaker.” I’m not: Days after he won his gavel in a protracted fight with hard-right Republicans, Speaker Kevin McCarthy gushed to a friend about the ironclad bond he had developed with an unlikely ally in his battle for political survival, Representative Marjorie Taylor Greene of Georgia. “I will never leave that woman,” Mr. McCarthy, a California Republican, told the friend, who described the private conversation on the condition of anonymity. “I will always take care of her.” Such a declaration from Mr. McCarthy would have been unthinkable in 2021, when Ms. Greene first arrived on Capitol Hill in a swirl of controversy and provocation. A former QAnon follower who had routinely trafficked in conspiratorial, violent and bigoted statements, Ms. Greene was then widely seen as a dangerous liability to the party and a threat to the man who aspired to lead Republicans back to the majority — a person to be controlled and kept in check, not embraced. But in the time since, a powerful alliance developed between Ms. Greene, the far-right rabble-rouser and acolyte of former President Donald J. Trump, and Mr. McCarthy, the affable fixture of the Washington establishment, according to interviews with 20 people with firsthand knowledge of the relationship, many of whom spoke on the condition of anonymity to discuss it. Their political union — a closer and more complex one than has previously been known — helps explain how Mr. McCarthy rose…