Maryland’s Attorney General Anthony Brown said he’s been watching the legal developments surrounding President Donald Trump’s use of the National Guard in U.S. cities and preparing in case Trump follows through on plans to send troops to Baltimore.

The Democrat and military veteran is the state’s top lawyer and has the power to sue the federal government on behalf of Marylanders.

Brown said he was encouraged by a California district court judge’s “good ruling” to keep a state’s military from policing civilians.

Judge Charles Breyer said the Republican president violated a longstanding federal law when Guard troops he deployed to Los Angeles to protect federal personnel and buildings started doing the work of cops.

Though Breyer did allow Trump to keep troops stationed in Los Angeles, his decision signals the court putting limits on the president’s use of military personnel.

The Trump administration appealed Breyer’s decision Thursday. But cases, like the one in California, can provide a legal roadmap for judges in other states should they face similar decisions.

“It doesn’t apply in Maryland, but it’s persuasive,“ Brown said.

Meanwhile, Brown said he’s had conversations with Gov. Wes Moore and Baltimore Mayor Brandon Scott, and more frequent communications with their top legal advisers, to game out legal scenarios should the president send the Guard to Baltimore.

Since Trump’s inauguration, Brown and his team have joined or filed dozens of lawsuits with other states’ attorneys general opposing the Trump administration’s policy decisions. Just as he has in other cases, he and his lawyers, along with the governor and the mayor, will discuss what’s best for Marylanders.

“This situation is no different,” he said of the possibility of military personnel on a Maryland city’s streets, acknowledging that his office may be Maryland’s first line of defense.

“We’re doing our homework,” he said. “We’re analyzing the law.”

Here’s what to know about what the California ruling could mean for Maryland.

Why did Trump send the Guard to California?

In June, the Trump administration took over, or federalized, California’s National Guard to protect federal personnel carrying out immigration enforcement operations and to protect federal buildings from protesters opposed to their actions.

The Department of Defense argued that federal law allowed for those uses.

And up until Tuesday’s ruling, the courts had sided with the Trump administration’s reasons for placing them there over the protests of their commander-in-chief, Gov. Gavin Newsom.

What did the judge decide?

Breyer’s ruling partially sided with Newsom and with Trump.

Breyer found fault with the Trump administration’s use of the Guard. He said they crossed a line when they started acting as law enforcement.

Trump can keep Guard troops in Los Angeles to protect federal personnel while they conduct immigration enforcement and to guard federal buildings, but they can’t color outside those lines.

What is Trump’s plan?

So far there’s been no official plan announced for the deployment of troops in Baltimore, according to federal and state officials. A spokesperson for the Maryland National Guard said they have not received any federal mobilization orders.

What has people worried is that Trump keeps threatening to send troops into cities with high crime rates and frequently mentions Baltimore.

On Tuesday, Trump said he “has the right” to send troops to Chicago to help fight crime and an obligation to keep people safe after the city experienced several homicides and dozens of shootings over the Labor Day weekend.

Trump said he would direct the National Guard to Chicago over the objections of city and state leaders. Then he referenced Baltimore.

“We’re going to do it anyways. We have the right to do it because I have the obligation to protect this country. And that includes Baltimore.”

The president didn’t make clear what he meant to do in Baltimore, and the White House declined to clarify Trump’s remarks. A spokesperson for the Department of Defense said they had “nothing to add” about the president’s Baltimore comments.

What have the governor and the mayor said?

Both Moore and Scott have opposed Trump’s plans to send Guard personnel to Baltimore but have welcomed federal funds, help getting ghost guns off the streets and more officers from federal agencies, such as the Bureau of Alcohol, Tobacco, Firearms and Explosives and the Federal Bureau of Investigation.

The state’s top officials have said that while they understand there’s more progress to be made in Baltimore when it comes to crime, sending in the National Guard isn’t the answer. Moore and Scott have applauded partnerships between communities and law enforcement for bringing down the homicide rate and number of nonfatal shootings to record lows.

The president’s persistent threats over the past several weeks have Moore and Scott weighing their legal options should military boots hit the ground. And both have acknowledged that they’ve conferred with Brown.

Can Trump deploy troops to Baltimore?

Yes, but the president should need a governor’s permission or a legal reason to commandeer a state’s National Guard. Trump has proven to be a president who acts first and leaves it up to others to sort out the details later.

In sending troops to Los Angeles, Trump cited a federal law but did not seek or have Newsom’s permission.

Trump’s deployment of troops in D.C. is different. The District of Columbia is not a state and the president controls the Guard. The District’s Attorney General Brian Schwalb filed a lawsuit Thursday challenging Trump’s use of the Guard for law enforcement purposes.

There are a few exceptions under federal law in which a governor’s permission is not required for the president to takeover a state’s troops, such as deploying them overseas.

Another is if the president invokes the Insurrection Act, but this is only used in times of extreme crisis. Military and civilian experts argue that these conditions do not exist in Baltimore or Chicago.