With each new controversy, Donald Trump’s opponents plead with Republicans to denounce him. Hasn’t Mr. Trump broken from GOP orthodoxy on free trade, immigration and entitlement reform? Not to mention the personal scandals and the never-ending tweets. Why do Republican leaders hesitate to rebuke him?

A shallow answer is politics: Sens. Jeff Flake and Bob Corker both tangled with Mr. Trump, and it turned out to be political suicide. But to get a deeper answer, it’s instructive to examine what Mr. Trump hasn’t done. Since the campaign, Mr. Trump has abandoned many of his previous positions and embraced traditional conservative views.

• Spending and taxes. During the election, Mr. Trump promised a $1 trillion infrastructure plan. Some Republicans feared his first initiative on taking office would be a pork-laden spending package reminiscent of Barack Obama’s stimulus bill. They also worried he would cut a deal with Democrats to raise taxes. “I am willing to pay more,” Mr. Trump said in May 2016. “And do you know what? The wealthy are willing to pay more.” Instead, the reverse happened: There’s no infrastructure plan in sight, except for the border wall, and Mr. Trump signed a sweeping bill to reduce personal and corporate taxes.

• Court nominees. In 2015 candidate Trump said his sister, a liberal federal judge, would be a “phenomenal” Supreme Court justice, though he claimed he had been joking. After Justice Antonin Scalia died, Mr. Trump decided to release a list of potential replacements. This was a central reason many conservatives voted for him. In appointing Justice Neil Gorsuch, President Trump made good on his promise. Since then, constitutionalists have cheered the quality and sheer quantity of his appointments to all levels of the judiciary.

• Abortion. In a successful effort to win the Iowa caucuses, Sen. Ted Cruz attacked Mr. Trump’s “New York values.” A Cruz TV ad showed Mr. Trump years earlier calling himself “pro-choice in every respect.” Yet President Trump has reinstated Reagan’s “Mexico City policy,” which prohibits federal funds from going to international groups that provide or promote abortions. Mr. Trump is also moving to require a hard division between abortion providers and clinics that take federal Title X funds, which would be a significant hit to Planned Parenthood.