WASHINGTON — U.S. President Donald Trump had more confrontational words for NATO as he departed Tuesday for Europe, suggesting his summit with Russian leader Vladimir Putin could be the “easiest” visit of the four-country trip.

The president spoke with reporters as he left the White House for Brussels, where his meeting with allies is expected to be marked by disagreements over trade, military spending and fears that Trump’s Helsinki summit with Putin will be friendlier.

“So I have NATO, I have the U.K. — that’s a situation with turmoil. And I have Putin. Frankly, Putin may be the easiest of all,” Trump said. After Brussels, Trump visits London.

Trump said the U.S. is “being taken advantage of by the European Union. We spend 75 percent on NATO and frankly, it helps them more than it helps us.” He has been pressing NATO countries to fulfill their goal of spending 2 percent of their gross domestic product on defense by 2024.

Although the U.S. intelligence community concluded Russia interfered in the 2016 election to boost Trump’s candidacy, and warns of further attempts at interference both in the 2018 midterms and in European elections, Trump would not say whether he considers Putin a friend or foe.

“I really can’t say right now. As far as I’m concerned, he’s a competitor,” Trump said. “I think that getting along with Russia, getting along with China, is a good thing.”

The meeting will be closely watched to see whether Trump will rebuke or embrace Putin, who has repeatedly denied the allegations of election meddling, in spite of evidence to the contrary.

In the midst of the scrutiny Tuesday, 44 House Democrats on the Armed Services and Foreign Affairs committees announced some guardrails for Trump ahead of the meetings — though it seems unlikely he will take heed — that revealed fears of concessions Trump might make.

Trump, they said, must recognize the importance of America’s military presence in Europe and the joint exercises that undergird NATO in deterring Russia and ensuring military readiness. “He must not weaken this posture or suspend or cancel these crucial activities, nor emulate Russian propaganda attempting to discredit them,” the statement reads.

They cautioned Trump to continue to affirm America’s commitment to NATO’s mutual self-defense clause and its open-door policy to new members, while taking a stand against Russia’s meddling in U.S. elections and in favor of Ukraine’s sovereignty over Crimea. U.S. law bars military-to-military cooperation with Russia, they wrote.

“The future of the Atlantic alliance and the international order, which has helped make the world safer and more prosperous, is at stake,” the statement reads.

It remains to be seen how easily Trump, a self-described master deal-maker, will fare against Putin, who has spent 18 years on the world stage.

In the talks, Trump will be unable to deliver on some things Putin may want, according to Olga Oliker, director of the Russia and Eurasia Program at the Center for Strategic and International Studies. Credible legitimization of its annexation of Crimea would require European allies to accede; an easing of U.S. sanctions on Russia would require Congress to reverse popular legislation; and a solution in Syria would require buy-in from various Middle Eastern powers.

That said, restarting military-to-military contacts with Russia is a relatively easy step and would be valuable in Syria, as would any advance toward an agreement for a United Nations-backed peacekeeping force in Ukraine, Oliker said.

For a big win, key nuclear arms control treaties, like the 2011 New START agreement and the 1987 Intermediate-Range Nuclear Forces Treaty, may be the most fertile ground, Oliker said.

New START restricts both the U.S. and Russia to 1,550 deployed strategic nuclear warheads on a maximum of 700 deployed intercontinental ballistic missiles and strategic bombers. In Trump and Putin’s first call in 2017, Putin raised the possibility of extending the New START treaty by another five years beyond 2021, but Trump reportedly brushed aside the offer, saying New START was a bad deal.

“You’d have to sell it to the president as a good treaty, even though someone else negotiated it. That’s been hard lately,” Oliker said.

Both the U.S. and Russia have accused each other of violating the INF Treaty, which calls for eliminating stockpiles of ground-launched and nuclear cruise missiles with a range of between 500 and 5,500 kilometers. At least one Pentagon official suggested the U.S. forego a planned sea-launched nuclear cruise missile as a bargaining chip to bring Russia back in line with the INF Treaty.

In the talks, the real danger zone for Trump is pulling the U.S. out of joint NATO exercises in Europe, as it would signal a profound unraveling of the 69-year-old alliance. With one stroke, Trump could ratchet up existing tensions with Europe and force U.S. allies to contemplate a future without U.S. investment in European defense — “for as long as this administration lasts, or forever,” Oliker said.

“I wouldn’t put anything past them,” Oliker said of the Trump administration, “but this would be very damaging to U.S.-European relations. It is central to NATO.”

While Moscow may on some level favor NATO falling apart, the alliance does preserve peace on the continent.

“If European countries start building up as the European countries, you’re back in the 19th and early 20th century,” Oliker said. “And I’d argue that period wasn’t all that good for [Russia].”

The Associated Press contributed to this report.