Thousands of protesters packed Times Square on Thursday evening to demonstrate against President Trump firing Attorney General Jeff Sessions — a move they view as a threat to special counsel Robert Mueller’s investigation into the 2016 Trump presidential campaign.

The crowd of about 4,000 formed in Times Square at about 5 p.m. and headed south on Broadway toward Union Square.

Some held signs that read “Trump is not above the law” and “Protect Mueller!” The crowd also chanted “No excuse! Must recuse!” as they rallied in Times Square, according to video of the protest.

The rally was one of several demonstrations in US cities including Boston, Baltimore, Chicago and Washington, DC, dubbed “ProtectMueller” marches.

They were organized by Move On advocacy group, who wrote in a statement announcing the marches: “Donald Trump has installed a crony to oversee the special counsel’s Trump-Russia investigation, crossing a red line set to protect the investigation.”

The marches formed a day after Trump fired Sessions, who had recused himself of the investigation into possible collusion between the Trump campaign and Russian government agents.

Trump named Matthew Whitaker as acting attorney general after firing Sessions – a move Trump critics viewed as an attempt to shut down or interfere with Mueller’s probe.

Whitaker had previously been critical of Mueller’s investigation, writing in a 2017 op-ed for CNN: “It is time for [Deputy AG Rod] Rosenstein, who is the acting attorney general for the purposes of this investigation to order Mueller to limit the scope of his investigation to the four corners of the order appointing him special counsel.”