MIAMI — President Trump is expected on Tuesday to announce his nominee for the Supreme Court seat vacated by the death of Justice Antonin Scalia. Many conservatives argue that a jurist who replicates Justice Scalia’s approach to law should fill the vacancy. Mr. Trump appears to agree, having vowed to nominate federal judges “in the mold of Justice Scalia.”

While Justice Scalia was a brilliant and ardent defender of conservatism, achieving a restoration of the original meaning of the Constitution — particularly its separation of powers — could be more quickly and effectively achieved by a nominee whose approach is more aligned with that of Justice Clarence Thomas.

The demeanors of the two justices could not have been more divergent. Justice Scalia was a firebrand known for opinions that were eloquent but often acerbic. Justice Thomas’s quieter disposition — he rarely asks questions at oral arguments — camouflages an equally deep and tenacious intellect.

What matters most, however, is not a justice’s demeanor but his judicial philosophy. On this score, Justice Thomas’s originalism is unflinching. In Gonzales v. Raich (2005), for example, a majority of the court held that state medical marijuana laws are pre-empted because the federal Controlled Substances Act is a valid exercise of Congress’s power to regulate interstate commerce. Justice Thomas dissented, asserting that if Congress can regulate individuals’ ability to grow, possess or use marijuana for personal medicinal use, “it can regulate virtually anything,” and states will be left with little power.