Updated at 2:04 p.m. ET

President Trump is celebrating America's oldest alliance, with French President Emmanuel Macron. But even as they prepare for a lavish state dinner, the two leaders could not paper over stark differences on issues such as trade and the Iran nuclear deal.

Macron is the first of two European leaders Trump is hosting this week. German Chancellor Angela Merkel will be in Washington, D.C., on Friday. Both France and Germany joined the U.S. in a six-nation pact with Iran to halt its nuclear program in exchange for sanctions relief. Trump has threatened to pull the U.S. out of that deal. Macron and Merkel want him to stay in.

"People know my views on the Iran deal. It was a terrible deal. It should have never, ever been made," Trump said Tuesday during an Oval Office photo opportunity with Macron. "It's insane. It's ridiculous. It should have never been made."

Trump has to decide next month whether to reinstate the economic sanctions that were lifted under the nuclear deal. He didn't explicitly say he would do so but warned, "If Iran threatens us in any way, they will pay a price like few countries have ever paid."

Macron argues the nuclear agreement is worth preserving, even as he tries to address Trump's concerns over Iran's ballistic missile program and its provocative actions in countries such as Syria and Yemen.

"It's not about tearing apart an agreement and having nothing," Macron said through an interpreter. "It's about building something new that will cover all of our concerns."

Despite their evident personal chemistry, Trump and Macron have significant policy differences. In addition to the Iran nuclear deal, Macron wants a permanent exemption from the president's new steel and aluminum tariffs. And he would like to see a more lasting commitment from the U.S. to stabilization efforts in Syria.

Macron acknowledged the global trade problems that have been created by an oversupply of steel and aluminum — but most of that glut is a product of China, not France.

Trump promised no immediate relief from the tariffs. He complained that even though two-way trade between the U.S. and France is relatively balanced, the European Union imposes too many barriers to U.S. exports. Last year, the U.S had a $14 billion trade deficit with France and a $102 billion trade deficit with the EU.

Military forces from France and the U.K. joined the U.S. in launching airstrikes on Syria earlier this month in retaliation for a suspected chemical weapons attack. But Trump is impatient to withdraw U.S. troops from that country as quickly as possible.

"I would love to get out. I would love to bring our incredible warriors back home," Trump said. "But I want to come home also with having accomplished what we have to accomplish."

Trump also hinted during the White House news conference with Macron that his embattled nominee to head the Department of Veterans Affairs, Ronny Jackson, may soon withdraw.

"I told Admiral Jackson just a little while ago, I said, 'What do you need this for?' " Trump said.

Some have questioned whether Jackson, a Navy admiral who serves as Trump's personal doctor in the White House, has the managerial skills needed to head such a large department. He has also been accused of inappropriate behavior.

Macron has skillfully courted Trump, inviting the U.S. president to be his guest last year at an elaborate military parade marking Bastille Day in Paris. Trump was so impressed that he ordered his own military parade this November, marking the 100th anniversary of the end of World War I.

The two presidents and their wives celebrated the wartime alliance between the U.S. and France on Monday by planting an oak tree on the South Lawn of the White House. The sapling comes from Belleau Wood, where more than 9,000 Marines died in the final months of WWI, according to a White House statement.

Later, the two couples took a sightseeing helicopter tour of Washington and then held a private dinner at George Washington's historic Mount Vernon estate.

The visit will include the Trump administration's first state dinner. The White House has been decorated for the event with cherry blossoms, sweet peas and white lilacs. The menu is American with French influences: spring lamb and jambalaya.

On Wednesday, Macron is set to address a joint session of Congress.

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