Charleston, a port city draped in Spanish moss and history, and surrounded by rivers and marshland in South Carolina’s Lowcountry, is intensely vulnerable to the effects of climate change. The sea level nearby has already risen a foot. Severe storms and flooding have dramatically increased.

So Charleston sued.

The city is one of numerous states and communities suing the world’s biggest oil companies, claiming they misled the public about the dangers of climate change. But Charleston’s case is unusual. The city has a new Republican mayor, who has let the lawsuit proceed. And the state of South Carolina — also Republican-controlled — strongly opposes the lawsuit.

This week the case faces a major test.

On Thursday and Friday, lawyers for Charleston and the oil companies are scheduled to face off in state court. Among the points to be discussed is President Trump’s executive order in April calling lawsuits like these a threat to national security.

Since that declaration, the Trump administration has launched a broad new attack against climate lawsuits. The Justice Department recently took the unorthodox step of pre-emptively suing Hawaii and Michigan to try to prevent them from even filing suits of their own.

The judge in Charleston’s case, Roger M. Young Sr., will hear arguments about whether it deserves to proceed to trial. He has also asked each side to weigh in on the implications of Mr. Trump’s executive order.

In recent years, the city has become a magnet for tourists and new residents drawn to the well-preserved antebellum mansions, walkable downtown and high-end hotels, shops and restaurants. Horse-drawn carriages take visitors on historical tours of the tree-lined cobblestone streets. Nearby historical sites include Fort Sumter, where the first Civil War shots were fired. The city is home to the Spoleto Festival, the global arts event, and to the International African American Museum, which examines the city’s role in the slave trade.