By Marc A. Thiessen

Special to The Washington Post

President Donald Trump just returned from a foreign trip that was the single most successful eight-day stretch of his presidency. But almost as soon as he landed at Joint Base Andrews, he abandoned the approach that gave him his best week in office, and returned to the form that gave him some of his worst weeks — tweeting against “fake news writers” and opining about how “Russian officials must be laughing at the U.S.”

Trump needs to ask himself: What made his trip so successful? For more than a week, he did not mention James B. Comey, Russia or “fake news.” Instead, he delivered a widely hailed address in Saudi Arabia where he pointed out that 95 percent of the victims of terrorism are Muslims and rallied the leaders of 50 Muslim nations to confront the terrorist threat. He brokered a massive arms deal with Saudi Arabia and forged the beginnings of a new regional alliance to confront the Islamic State and Iran. He became the first sitting American president to visit the Western Wall in Jerusalem and pledged to launch a new effort to forge Israeli-Palestinian peace. He had a cordial meeting with Pope Francis and urged NATO nations to finally meet their financial commitments to the alliance. He deftly smoothed a diplomatic row with Britain over the U.S. leak of intelligence on the Manchester, England, bombing.

The result? Critics were reduced to spreading false reports that he was not using his translation earpiece (actual “fake news”), criticizing his body language at photo ops and speculating about whether the first lady smacked away his hand at an arrival ceremony. They seemed small and petty while Trump was serious, substantive and — dare we say it — presidential.

Yes, some on the left were apoplectic about Trump’s refusal at the Group of Seven summit to endorse the Paris agreement on climate change. So what? They were also apoplectic when President George W. Bush withdrew from the International Criminal Court and the Anti-Ballistic Missile Treaty. If Trump is being attacked hysterically for being a conservative, rather than for his tweets, he’s winning.

Now that he’s back, Trump needs to decide: Does he want the next four years to be like his foreign trip, or does he want to return to the morass of controversy he left behind when Air Force One took off for Riyadh, Saudi Arabia? If it is the former, then the answer is simple: Keep doing what he was doing on the trip. Thereis no reason he has to be on foreign soil to embrace the power and grandeur of the presidency. What worked abroad can also work at home.

Washington is a jungle, but as president, Trump is the king of the beasts. He needs to stop fighting with the lesser animals. One of the secrets of the presidency Trump has been slow to embrace is that the office confers a certain majesty on its occupants. There is a reason the opposing party’s response to a State of the Union address invariably falls flat compared with the real thing. Trump’s most successful moments — his terrific address to Congress, his nomination of Neil M. Gorsuch for the Supreme Court, his foreign trip — all came when he embraced the dignity of the office. His worst moments came when he did not.

The lesson should be clear: Stay above the fray, ignore your critics, focus on substance, and use the presidency to promote your agenda. Go on a tour to highlight the achievements of your foreign trip. Visit defense factories that will get jobs because of your Saudi arms deal. Speak to Jewish organizations about your visit to Israel and plans to isolate Iran, defeat the Islamic State, and bolster the U.S.-Israel alliance. Barnstorm the country promoting your agenda. And never mention Comey or the Russia probe — not in an interview, not in a tweet.

Trump does not need the tactics of the campaign to succeed in the Oval Office. The presidency is more powerful than any of the tools that got him into the office. He needs to stop acting like a candidate for president and start being who he really is: president of the United States.

Marc Thiessen, a fellow with the American Enterprise Institute and former chief speechwriter to President George W. Bush, writes a weekly column for The Washington Post.