It was encouraging to see George Stephanopoulos raise the issue of judicial appointments Sunday on ABC's This Week. "What kind of judges will you appoint? Will they be conservative? What does that mean to you and how will you ensure it?" he asked Donald Trump.

When Trump replied that he would "appoint conservative judges," Stephanopoulos asked for examples. Trump cited Justice Clarence Thomas and noted that Justice Roberts "turned out to be an absolute disaster because he gave us ObamaCare." Trump added that he would "work with people that I respect, conservative people" in selecting judicial nominees.

Because Donald Trump does not have any experience appointing judges, his best approach to the process would indeed be to rely heavily on the recommendations of respected conservatives in the legal community. Other GOP contenders have the legal background to take a more hands on approach.

There is no one right answer, but questioning the presidential candidates about judicial appointments is vitally important. Stephanopoulos did well, going beyond asking Trump what kind of judges he would appoint by prodding him for specific examples. Most importantly, he asked the Republican candidate how he would ensure that his judicial nominees are truly judicial conservatives.

The importance of that last question was emphasized last June with the most activist end of a Supreme Court term in recent memory, made possible by Republican Supreme Court appointees, Chief Justice John Roberts and Justice Anthony Kennedy.

For the second time in three years, Chief Justice Roberts saved ObamaCare by rewriting the statute. At the same time, Justice Kennedy, a Reagan appointee, rubbed salt in what was already deep wounds of conservative disappointment by further involving the government in the marriage business and discovering a cause of action for "disparate impact" discrimination in the 1968 Fair Housing Act.

The latest headlines on the 2016 elections from the biggest name in politics. See Latest Coverage →

Regardless of your views on ObamaCare, marriage, and disparate impact theories of discrimination, those three decisions in June 2015 should be disturbing because they remind us that there are virtually no limits on the Supreme Court's power to act as "the Ruler of 320 million Americans coast-to-coast," as Justice Scalia observed in the marriage case.

Over the past 50 years, a Democratic president has never failed to fill a Supreme Court vacancy with an appointee who was and remained a reliable liberal vote on the hot-button issues before the Court.

Roberts and Kennedy – along with retired Justices Stevens, Souter, and O'Connor – make it painfully clear that Republican presidents do not have the same record with respect to conservative appointees.

With several Supreme Court vacancies looming and hundreds of lower court appointments facing the next president, it is of utmost importance that the GOP presidential candidates articulate what procedures they would follow to ensure that the failures of past presidents are not repeated.

What is the best way to identify a nominee who will remain committed to conservative judicial principles and the constitutional limits on government if placed on the federal bench? I believe the core characteristic GOP presidents should look for is the courage and commitment to follow the Constitution and laws where they lead, even when they lead to an inconvenient, uncomfortable or politically incorrect place.

A long judicial record of constitutionalism – something Alito had but Roberts did not – is an important piece of evidence. But it is not the only predictor of judicial courage. That quality can be demonstrated on or off the bench.

Again, there is no single right answer. What's important for now is that we hear from all the GOP hopefuls about how they would approach the challenge of filling judicial vacancies. What specific steps will they take in selecting nominees? What characteristics will they look for? What questions will they ask potential nominees? 

Curt Levey is a constitutional law attorney and executive director of the FreedomWorks Foundation. He can be reached on Twitter at @Curt_Levey.