Hundreds demonstrated on Boston Common Thursday night in response to the resignation of Attorney General Jeff Sessions. Protesters say Sessions' ouster was a move by the White House to interfere with Special Counsel Robert Mueller's investigation into possible collusion between Russia and the Trump campaign in the lead-up to the 2016 presidential election.

Also on the Common was former Secretary of State John Kerry.

"I think the president is trying to shut down this investigation, trying to create problems for it," Kerry told WGBH News. "He wants to hide it, and he's put somebody in there [as attorney general] who is an insult to everybody who's ever been in law enforcement or is in it today."

Demonstrators called on newly-elected and re-elected members of Congress to protect Robert Mueller's probe. Samuel Pierce of Dorchester, who spoke at the protest, singled out two Massachusetts politicians in particular.

"Elizabeth Warren, we're sending her back to D.C.. We're sending a lady named Ayanna Pressley to Washington D.C.. These are the people that not only are in the Massachusetts congressional delegation but are going to be household names when we start the impeachment process," he said.

After the common had been cleared, David Lydon, a 32-year-old Trump supporter from Dorchester, arrived to stage a one-man counterprotest. Lydon told WGBH News that progressive activists were jumping to conclusions about the meaning of Sessions' resignation.

"Sessions resigned," Lydon said. "[Trump] could have told him to beat it and then got fired, okay? Sessions was a lame duck attorney general. He did absolutely nothing. He recused himself from jump street."

When asked if he had any concerns about the Mueller investigation, Lydon said, "No. Because if they had something they would have produced something. ...I could bet everything I own that there will be nothing on President Trump."

Organizers of the Boston demonstration and those organizing others across the country disagree, and say if Mueller is removed from the probe they are prepared to march on Washington in massive numbers.