After Special Counsel Robert Mueller's 400-page report detailed numerous instances in which President Donald Trump may have attempted to obstruct justice, progressive lawmakers and advocacy groups on Thursday made the case that it is the duty of Congress to begin impeachment proceedings.

"Mueller's report is clear in pointing to Congress' responsibility in investigating obstruction of justice by the president," tweeted Rep. Alexandria Ocasio-Cortez (D-N.Y.). "As such, I'll be signing onto Rashida Tlaib's impeachment resolution."

Formally introduced last month, Tlaib's resolution directs the House Judiciary Committee to immediately begin investigating whether Trump "committed impeachable offenses."

Ocasio-Cortez went on to acknowledge the political tensions surrounding the impeachment issue, but concluded Mueller's report "squarely puts this on our doorstep."

Ocasio-Cortez's call for an impeachment probe—which was joined by Reps. Ayanna Pressley (D-Mass.), Ilhan Omar (D-Minn.), Al Green (D-Texas), and others—came after House Majority Leader Steny Hoyer (D-Md.) quickly dismissed the growing demand for impeachment proceedings, saying they would "not worthwhile at this point."

The Washington Post's Greg Sargent denounced Hoyer's remarks as "straight-up abdication" and "dereliction of basic duty."

House Speaker Nancy Pelosi (D-Calif.), who has previously said moving to impeach Trump is "just not worth it," announced following the Mueller report rollout that the House Democratic caucus will hold a conference call Monday to discuss the special counsel's findings.

Progressive advocacy groups argued there's no reason for delay.

"We will not treat this as normal," MoveOn said in a petition that has garnered nearly 160,000 signatures. "And politicians in Washington must not continue to conduct business as usual. Everyone in Congress must look in the mirror and decide how they will fulfill their oath to defend our Constitution—and which side of history they want to be on."

Credo Mobile echoed this call in a petition of its own, demanding that House Democrats "immediately act to defend our democracy" by launching impeachment hearings against both Trump and Attorney General William Barr, who was accused of acting as the president's personal lawyer during a press conference ahead of the Mueller report's release.

"Speaker Pelosi and House Democrats have a choice to make, and the path they choose will speak volumes about their commitment to our democracy and to the communities Trump threatens every day: Will they continue to play politics as usual or will they step up to use their power to impeach both Donald Trump and William Barr?" Credo's petition reads.

In an open letter to House Democrats on Thursday, The Intercept's Mehdi Hasan argued Mueller's findings provide "a clear and detailed road map for impeaching Donald Trump."

Citing the Mueller report's statement that "Congress has authority to prohibit a president's corrupt use of his authority in order to protect the integrity of the administration of justice," Hasan wrote: "[T]he time for waiting is over. And the moment for impeachment hearings has arrived."

"Look, I get it. You're afraid," he added. "You're afraid of the backlash from your Republican counterparts. You’re afraid of losing in the Senate, where—right now—you lack a majority to convict Trump. You're afraid that impeachment hearings will distract from your party's 2020 presidential campaign. But your job, first and foremost, is to preserve democracy and protect the rule of law. That's the job assigned to you by the Constitution and also what's expected of you by the American people. You cannot walk away from it."