The war in Ukraine was top of U.K. Prime Minister Rishi Sunak’s agenda Wednesday as he started a two-day trip to Washington carrying the message that post-Brexit Britain remains an essential American ally in a world of emboldened authoritarian states.

The U.S. and U.K. are the two biggest military donors to Ukraine, and the war will be the focus of Sunak’s meeting Thursday at the White House with President Joe Biden.

The breaching of a major dam in southern Ukraine, which sent floodwaters gushing through towns and over farmland, has given the subject added urgency. Neither Washington nor London has officially accused Russia of blowing up the Kakhovka hydroelectric dam.

Sunak said Wednesday that U.K. intelligence services are still assessing the evidence, but “if it does prove to be intentional, it will represent a new low … an appalling barbarism on Russia’s part.”

“Russia throughout this war has used as a deliberate active strategy to target civilian infrastructure,” he told broadcaster ITV in Washington.

Britain and the U.S. are lead players in an international effort to give Ukraine F-16 fighter jets, and talks are also likely to include extra air defense measures against Russian bombardment as Ukraine launches a counteroffensive to retake occupied territory.

Sunak began his visit by laying a wreath at the Tomb of the Unknown Soldier in Arlington National Cemetery to mark U.S.-U.K. military ties. The trip is Sunak’s first to the U.S. capital since he took office in October, but his fourth meeting with Biden in as many months. The two leaders have crossed paths at a Group of Seven summit in Japan, in Northern Ireland and at a three-way defense meeting with Australia in San Diego.

Sunak, 43, and 80-year-old Biden are very different politicians. Sunak is an heir of free marketeer Prime Minister Margaret Thatcher, and wary of big government interventions in the economy such as Biden’s Inflation Reduction Act, a huge package of tax breaks and subsidies aimed at boosting green industries.

But he’s also pragmatic, and has restored stability to Britain’s government after the turbulent terms of predecessors Boris Johnson and Liz Truss.

Johnson championed the populist Brexit movement and led Britain out of the European Union, a decision Biden has made clear he thinks has hurt the U.K. Truss was in office for less than two months, resigning after her rash tax-cutting plans sparked a financial crisis.

Sunak, who was chosen by the governing Conservatives to replace Truss, has reassured Washington by smoothing relations with the EU, striking a deal with Brussels to resolve a long-festering dispute over Northern Ireland trade.

In his meeting with Biden, Sunak will push for closer economic ties between the U.S. and U.K., arguing that economic cooperation is as crucial to security as defense alliances.

“Just as interoperability between our militaries has given us a battlefield advantage over our adversaries, greater economic interoperability will give us a crucial edge in the decades ahead,” Sunak said ahead of the talks.

A British government official who previewed Sunak’s agenda on condition of anonymity said Sunak wants to discuss ways to protect supply chains from hostile actors and how to ensure China doesn’t corner the market on producing semiconductors and other key parts.

He won’t, however, push for a U.K.-U.S. free trade agreement. U.K. officials accept that long-cherished goal of Brexit supporters is currently on ice.

Sunak, a Stanford University MBA graduate who dreams of creating a British Silicon Valley, also wants to discuss the promise and perils of Artificial Intelligence. He’s eager to make sure the U.K. is not excluded from U.S.-EU talks on the subject.

Sunak has floated an idea that the U.K. could be a center for regulating the fast-moving technology, though no major news on that front is expected during his trip.

The prime minister’s spokesman, Max Blain, said Britain’s approach to regulation, “agile and able to adapt with the fast pace of this technology, makes the U.K. well placed to take a leading role here.”

Sunak is also likely to lobby for U.K. Defense Secretary Ben Wallace to become the next head of NATO after Secretary General Jens Stoltenberg steps down in September. The prime minister is expected to stress that the next secretary-general should be someone who “carries on Stoltenberg’s good work of modernization but also understands the importance of defense spending at this critical time.”

The comment could be seen as a subtle dig at another possible contender for the post, Danish Prime Minister Mette Frederiksen, who met with Biden in Washington earlier this week. Denmark has lagged behind NATO’s target for members to spend 2% of gross domestic product on military budgets by 2030.

Sunak is also due to meet U.S. business executives and hold talks with congressional leaders, including Speaker Kevin McCarthy, on Capitol Hill. On Wednesday evening he’ll attend a Washington Nationals baseball game – though he won’t throw out the opening pitch, to the disappointment of the British media.

Sunak stressed he was never meant to throw out the pitch at the game, which includes military bands and a flyover to celebrate of U.S.-U.K. ties.

“My sport is more cricket than baseball, in any case,” he said.