Protesters gathered in major cities around the U.S. on Thursday over President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's firing of Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsGOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status MORE, rallying in support of Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE, the special counsel in charge of the investigation into Russian election meddling.

The hashtag "#ProtectMueller" was the top trending term on Twitter in the U.S. Thursday night as demonstrators gathered in Washington, D.C., New York and Boston, as well as other cities around the country.

Cleveland. Boston. Baltimore. NYC. Washington, DC. Omaha. Philadelphia. These crowds are massive EVERYWHERE.



Thousands are mobilized to #ProtectMueller and demand that #WhitakerMustRecuse. pic.twitter.com/C5P6lrDcX8 — Public Citizen (@Public_Citizen) November 8, 2018

A list of events hosted by the activist group Public Citizen listed dozens of events in smaller cities in nearly every state Thursday night as demonstrators protested what many thought to be an effort by the president to begin shutting down the Russia investigation.

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Sessions is set to be replaced by Matthew Whitaker as acting attorney general pending a permanent replacement to be confirmed by the Senate. Whitaker in the past has been a vocal opponent of the Mueller investigation.

Photos of events posted on Twitter showed hundreds of protesters gathered in various locations holding signs reading "Protect Mueller" and "Nobody is above the law."

Protests Thursday came hours after Arizona Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R), himself a frequent critic of the president, vowed to force a vote in the Senate on bill that would codify Justice Department regulations stating that only a senior DOJ official can fire the special counsel.

Trump has been critical of the Mueller investigation for months, deeming the probe which has ensnared several former members of his campaign in criminal charges as a "witch hunt" led by "angry Democrats."

Sessions had been expected to exit the Trump administration for months, and turned in his resignation to Trump on Wednesday just hours after Democrats retook the House in Tuesday's midterm elections.