When President Trump appointed his friend Steven Witkoff to be his Middle East envoy last November, the choice prompted head-scratching in diplomatic circles.

Many foreign officials had never heard of Mr. Witkoff, a billionaire New York real estate developer who has known Mr. Trump since the mid-1980s. The president’s new envoy not only lacked expertise in the region apart from some business dealings, he had no diplomatic experience.

That didn’t matter to a president who considers Washington credentials a liability and views foreign policy as a series of business transactions. And Mr. Trump was impressed by Mr. Witkoff’s ability to help the outgoing Biden administration seal a temporary cease-fire deal in Gaza between Israel and Hamas.

Now, in a fresh sign of confidence in his old friend, Mr. Trump has expanded Mr. Witkoff’s portfolio. As Mr. Trump pursues a peace deal in Ukraine and a potential realignment of U.S.-Russia relations, he has tapped Mr. Witkoff to be his personal envoy to Russia’s president, Vladimir V. Putin.

On Thursday morning, Mr. Witkoff landed in Moscow to meet with the Russian leader for the second time in just over a month. In mid-February, he and Mr. Putin sat down for a three-and-a-half-hour session that led to Mr. Putin’s release of Marc Fogel, an American serving a prison sentence in Russia on marijuana smuggling charges.

Engaging Mr. Putin is an assignment that would make even a seasoned diplomat take a deep breath. Befitting his past as an intelligence operative, the Russian leader is a master of intimidation, manipulation and deceit. Some experts and diplomats who know Mr. Putin fear that Mr. Witkoff may be in over his head.