(The Washington Post)

President Trump said Friday that he continues to believe torture methods can be effective to combat terrorism, but he pledged to defer over whether to implement such tactics to Defense Secretary James N. Mattis, who has opposed them.

“He will override,” Trump said in a joint news conference with British Prime Minister Theresa May at the White House. “I’m giving him that power.”

During his campaign, Trump had expressed support for enhanced interrogation techniques, in particular simulated drowning known as waterboarding, which was forbidden by the Obama administration. His vow to allow Mattis to set the direction for his administration on the issue came on a day when Trump planned to visit the Pentagon and sign new executive actions related to national security, including the fight against terror groups such as the Islamic State.

“I happen to feel that it does work. I’ve been open about that for a long period of time. But I am going with our leaders. And we’re going to — we’re going to win with or without, but I do disagree,” Trump said about “torture or waterboarding or however you want to define it.”

Trump’s meeting with May was his first with a foreign leader, a summit on trade and security that was being closely watched around the world. It represented a chance for the new American president to demonstrate his administration’s commitment to maintaining close relations with a key U.S. ally while pursuing new trade ties as Britain works to exit the European Union.

May sought to tie Trump more closely to the long-standing U.S.-European security alliance, saying her opening statement that the two leaders were “united in our recognition of NATO as the bulwark of our collective defense.”

Yet there were signs of potential differences. White House aides have said Trump, who is scheduled to speak with Russian President Vladi­mir Putin on Saturday, is considering lifting U.S. economic sanctions on Russia over its military incursion into Ukraine.

May declared at the news conference that she expects the sanctions imposed jointly by the United States and European countries to remain in place until Moscow abides by the Minsk agreement in 2104 to halt the hostilities.

“It’s very early to be talking about that,” Trump said when asked if he favored lifting the sanctions. “If we can have a great relationship with Russia and with China and with all countries, I’m all for that. That would be a tremendous asset.”

Trump grew defensive about his relationship with Putin, whom he has praised during the campaign as a stronger leader than former president Obama. Trump has said he is willing to work with Putin despite the assessments from U.S. intelligence agencies that Moscow meddled in the presidential elections to help him.

Though the president has acknowledge Russia’s involvement in the hacking of Democratic Party emails, Trump has insisted that he does not believe Putin’s regime wanted him to win.

“I don’t say good, bad or indifferent. I don’t know the gentleman,” Trump said of Putin on Friday. “I hope we have a fantastic relationship. That’s possible and it’s also possible that we won’t. We will see what happens.”

Trump emphasized that in talking with Putin, he would represent the American people “very, very strongly, very forcefully.” Referring to the Islamic State, the president added that “if we have a great relationship with Russia and other countries, and if we go after ISIS together, which has to be stopped -- that’s an evil that has to be stopped -- I will consider that a good thing, not a bad thing.”

Trump and May vaulted to power last year by speaking to similar strains of populist anxiety over broad global shifts in the economy and immigration that led voters to reject the status quo and take a gamble on forces who promised sweeping change. Trump’s skepticism toward international institutions and multilateral partnerships have raised questions abroad about the future of U.S. leadership on the world stage.

Trump used a prepared opening statement to deliver a forceful defense of “Brexit” — the British vote to leave the European Union. He cast the surprise victory of a populist referendum as a stroke for liberty.

“The United States respects the sovereignty of the British people and their right of self-determination,” Trump said. “A free and independent Britain is a blessing to the world.”

If that wasn’t a clear enough rebuke of the 28-nation European Union and its common market, Trump later praised Brexit as a building block for better trade relationship for Britain, and he noted that his own business dealings with what he called “the consortium” had been arduous and disappointing.

“I think Brexit’s going to be a wonderful thing for your country,” he told May, adding that Britain will be able to “make free trade deals without having somebody watching you.”

And he seemed to agree with political analysts who saw the Brexit vote in June as a harbinger of an anti-establishment, populist wave that carried him to victory five months later.

“Brexit was an example of what was to come,” he said.

Trump has sought to follow through on his promises of change in a whirlwind first week as he signed a flurry of executive actions meant to shake up the United States’s role internationally. He has withdrawn U.S. participation in a 12-nation Pacific Rim trade deal, ordered planning to begin on a border wall with Mexico and floated plans to block refugees and immigrants from Syria and other Muslim-majority countries.

“Now is the dawn of a new era of American independence, a rededication to the idea that the people are in charge of their own destiny,” Trump told Republican lawmakers at a congressional retreat in Philadelphia on Thursday.

His meeting with May, who replaced David Cameron in July, represented Trump’s opening bid to begin pursuing the sort of bilateral negotiations on trade and security that he prefers over the kind of multilateral partnerships that former president Obama favored.

In their first meeting, Trump and May both spoke of the “special relationship” between the United States and the United Kingdom. But when a BBC reporter asked Trump about worries in Britain over Trump’s support of torture, praise of Russia and potential ban on Muslim immigrants, Trump looked at May and joked: “This was your choice of a question?”

Drawing laughs from White House staff and reporters, Trump continued: “There goes that relationship.”

But the question highlighted that Trump’s rapid-fire moves since taking office have prompted a vocal backlash at home and abroad. Mexican President Enrique Peña Nieto on Thursday canceled a visit to the White House scheduled for next week.

Trump aides reacted by suggesting that the United States could pay for the wall, which is projected to cost billions of dollars, through a 20 percent import tax on goods from Mexico, a move that, if carried out, could spark a trade war with the United States’ third-largest trading partner.

On Friday morning, Trump and Peña Nieto spoke by phone for an hour, White House officials said.

Mexico “has out-negotiated us and beat us to a pulp through our past leaders. They’ve made us look foolish,” Trump said during the news conference. “I’m not going to let that happen.”

Anne Gearan, Ashley Parker and Philip Rucker contributed to this report.