Attorney General Maura Healey responded to the retirement of former Defense Secretary Jim Mattis, calling it a bad sign for the future of the country.

“General Mattis ... was looked to by so many people, across the board, across the aisle, as somebody to respect and admire that we could count on to sort of hold the line,” Healey said during an interview with Boston Public Radio Friday. "The fact that he has stepped down, the reasons, the purported reasons for his stepping down are incredibly troubling and serious.”

Mattis announced his resignation in a letter Thursday, criticizing president Donald Trump’s military judgment.

“My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues,” he wrote. “Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position.”

Trump is now threatening a government shutdown if Democrats don’t agree to fund a border wall between the United States and Mexico.

Healey said her office will continue to challenge the president on this and other issues.

“I’ve sued this president and his administration multiple times,” Healey said. “Why? Because he does things that are illegal, unlawful and hurt the people of our state. It’s as simple as that, and we’ll continue to be there.”

Healey emphasized the importance of federal agencies that could potentially be affected by a shutdown.

“There are some things that are happening that we can’t even quite get to that we’re going to have to spend years repairing and restoring,” she said. “Some of that goes right to the heart of the strength of our federal agencies, and right now they’ve had their hands tied, and I think that’s why someone like Gen. Mattis has said you know, I can’t continue to abide.”

In November, Trump sent 5,200 military troops to the U.S.-Mexico border in response to an incoming caravan of migrants from Central America.