President Donald Trump's first meeting with Germany's Angela Merkel at the White House on Tuesday will test the power dynamic between the West's two pre-eminent leaders, one struggling for credibility on the world stage while the other fights for political survival at home.

For months, Trump has accused Merkel of "ruining" Germany by accepting refugees and predicted voters would overthrow her, even while describing her as a great world leader. Merkel has reluctantly emerged as the main defender of the liberal global order that Trump has vowed to upend, as he unsettles European allies with protectionist threats, calls for higher defense spending and praise for Britain's vote to leave the European Union.

"This is one of the most important moments early in the Trump presidency," carrying major ramifications for Trump's relations with Europe and Russia's ambitions, said Nicholas Burns, a Harvard professor and former U.S. undersecretary of state.

The two are stylistic opposites, the U.S. president a flamboyant former reality-television star who is guided by instinct and thrives on unpredictability, the German chancellor a physicist by training who's known as methodical and persistent.

Merkel, an 11-year veteran of global summitry sitting at the table with her third U.S. president, has prepared by poring over old comments and videos of the real estate magnate. She can quote interviews Trump has given from memory, according to a German official.

When Merkel hosted Canadian Prime Minister Justin Trudeau for a private dinner last month in Berlin, she quizzed him for details about his Trump visit days earlier, according to a Canadian government official. In her hunt for insights, Merkel was struck by a Playboy magazine interview Trump gave in 1990 where he said he'd only run for president if he saw the U.S. "continue to go down the tubes."

"She's the kind of person who can turn on the persuasion in a one-on-one talk," said Juergen Hardt, the German government's coordinator for trans-Atlantic relations. "Her tone with Trump will be friendly."

Merkel, 62, has shunned the path of courting Trump with eager praise as U.K. Prime Minister Theresa May did. Unlike Japan's Shinzo Abe, she also won't have a chummy getting-to-know-you golf weekend at Mar-a-Lago. Her congratulations after Trump's surprise victory over Hillary Clinton came with a pointed statement suggesting caveats for the relationship if he strayed from both countries' commitments to freedom, law and respect for diversity of religion, race, gender and politics.

Trump wants to hear Merkel's views on dealing with Russian President Vladimir Putin and on prospects for peace in eastern Ukraine, a Trump administration official said Friday. On two initiatives championed by Merkel and Obama — a U.S.-EU trade pact and the Paris climate-change accord — the administration hasn't decided on its position yet, the official said.

For her part, Merkel plans to offer Trump a quiet tutorial on trade. She'll sketch her vision of a global trade agenda she sees at risk, pushing back against U.S. criticism of Germany's trade surplus and the euro's exchange rate, according to two German government officials. Above all, she will try to find a line in to Trump, one official said.

Merkel, who presides over Europe's biggest economy, can be combative on trade. After Trump suggested there's an abundance of Daimler AG's Mercedes-Benz cars on New York's Fifth Avenue, she responded last month by noting the number of Apple Inc. iPhones in use at a conference in Munich attended by U.S. Vice President Mike Pence.

"We're proud that we have good products, just as the Americans are proud that they have good products," Merkel said. BMW AG Chief Executive Officer Harald Krueger and Siemens AG CEO Joe Kaeser will be among German business leaders joining Merkel on the trip.

"Trump doesn't have a buddy in western Europe like he does in Asia; it will be interesting if that's a role Merkel will try to play," said James Carafano, vice president of the Heritage Foundation, a conservative policy center in Washington, who advised Trump's transition team. "Personal relationships are very important for Trump."

Merkel comes to Washington strengthened by a rebound in her popularity, even as polls suggest a close race with Social Democrat Martin Schulz in Germany's Sept. 24 election. She'll have plenty of opportunities to burnish her image when she hosts world leaders at the Group of 20 summit in Hamburg in July.

European leaders confronted with a weakening EU, Brexit, and a surge in populist movements will look for Trump to give Merkel assurances he truly believes in NATO and the EU, said Burns, who supported Hillary Clinton in last year's presidential election after serving under Republican and Democratic presidents during a 27-year diplomatic career.

If Trump doesn't reaffirm his support of Europe strongly enough he could face "significant" repercussions from congressional Republicans and destabilize trade and investment relations with European nations that collectively represent the largest U.S. trading partner and investor, Burns said.

"She may be the most important American ally in the world," Burns said of Merkel. "She's the most powerful leader in Europe by far. She's been the most effective blocking agent against Vladimir Putin."

The chancellor can rely on her dry wit and unassuming affability that helped her win over Trump's two predecessors. In addition to strong ties with Obama, Merkel established a rapport with George W. Bush, whom she visited at his ranch in Crawford, Texas.

This time might be more difficult. Although she's avoided direct confrontation with Trump, she condemned his first immigration ban, rejected accusations of currency manipulation and warned against seeking to foment EU divisions.

While Trump has said little about Merkel in his seven weeks in office, he has called the EU a "vehicle for Germany" and blasted Merkel's "insane" open-border refugee policy during the presidential campaign.

"I've had great respect for her. I felt she was a great, great leader," Trump said in an interview in January with The Times of London and Germany's Bild newspaper. "I think she made one very catastrophic mistake and that was taking all of these illegals."