President Donald Trump will be the guest of honor at the Bastille Day parade in Paris on Friday, marking the 100th anniversary of U.S. forces joining the fight against Germany in World War I.

This will be his second visit to Europe in two weeks, following his successful trip to Poland and the G-20 summit last week.

Trump and French President Emmanuel Macron will hold a bilateral meeting in Paris on Thursday and a working dinner at the Eiffel Tower that night.

Discussion will focus on a number of issues, including counterterrorism cooperation between the United States and France, the U.S.-led fight against the Islamic State in Iraq and Syria, trade, climate change, and the future of the transatlantic alliance.

Macron has been deeply critical of Trump over his decision to withdraw the United States from the Paris climate accord.

At the G-20, while not naming the U.S. president directly, Macron took another thinly disguised swipe at what he sees as the current trajectory of American foreign policy, declaring:

I will not concede anything in the direction of those who are pushing against multilateralism. We need better coordination, more coordination. We need those organizations that were created out of the Second World War. Otherwise, we will be moving back toward narrow-minded nationalism.

There will be significant disagreements between the U.S. and French leaders on a number of other issues as well, including the refugee crisis and Europe’s handling of it.

In his meeting with Macron, Trump should reiterate U.S. opposition to the Paris accord, standing firm in defending U.S. national sovereignty.

Trump should also call on France to increase its level of defense spending as a NATO member, which currently stands at 1.79 percent. France should meet the agreed minimum expenditure of 2 percent of gross domestic product on defense that is expected of all NATO members.

Trump must also use the opportunity of his Paris visit to voice strong U.S. opposition to plans in Brussels to develop a European Union army, which would undermine NATO and divert scarce resources away from the alliance.

In addition, Trump must underscore U.S. support for Britain’s exit from the European Union and the principles of self-determination and sovereignty in Europe.

Macron has been a fierce opponent of Britain’s exit from the EU, and has urged European Commission officials to adopt a hard-line stance in their two-year negotiations with the British government, a position that is extremely counterproductive.

Last week in Hamburg, Trump declared his strong support for a U.S.-U.K. free trade deal, a message he should continue to voice in France. Brexit will result in a stronger special relationship and a more powerful transatlantic alliance, and is in the interests of Great Britain, the United States, and Europe as a whole.

The United States and France must continue to work together in key areas of common interest, especially in ensuring the defeat of ISIS, standing up to Russian aggression in Eastern Europe, and preventing the rise of a nuclear-armed Iran.

But where there are clear policy differences and visions, the U.S. president should be willing to aggressively stand up for American interests and have a frank exchange of views with his French counterpart.

While President Barack Obama was content to lead from behind, Trump must be robust and assertive in projecting U.S. strength and resolve in Europe and on the world stage.