Intensifying pressure on Speaker Nancy Pelosi to act on her warning that President Donald Trump has sparked a constitutional crisis, 109 House Democrats have now expressed support for impeachment proceedings after four more lawmakers on Sunday joined the rapidly growing chorus.

According to Politico, more than a dozen members of the House Democratic caucus have called for an impeachment inquiry against Trump since Special Counsel Robert Mueller testified before Congress last week, including Rep. Katherine Clark (D-Mass.), a member of Pelosi’s leadership team.

Reps. Denny Heck (D-Wash.), Suzan DelBene (D-Wash.), Derek Kilmer (D-Wash.), and Kim Schrier (D-Wash.) announced via Twitter Sunday that they support impeachment proceedings against the president after reading Mueller’s report and listening to his testimony.

“Congress has a responsibility laid out in the Constitution to perform oversight,” said DelBene. “Further underscoring his disregard for the Constitution, the president has attacked the free press, ignored congressional subpoenas, and instructed his own staffers not to cooperate with ongoing investigations. With every act of defiance, he continues to disgrace his office and violate the checks and balances that are the foundation of the Constitution.”

Sen. Patty Murray (D-Wash.), the third-ranking Senate Democrat, also voiced support for an impeachment inquiry on Sunday, citing “threats to our democracy identified in Special Counsel Mueller’s report.”

Pelosi, the top Democrat in Congress, has thus far resisted pressure from the grassroots, her caucus, and her leadership team to launch an impeachment inquiry, claiming on several occasions that the House doesn’t need to launch hearings because Trump is already “self-impeaching.”

Rep. Jerry Nadler (D-N.Y.), chairman of the House Judiciary Committee, has also stopped short of publicly supporting formal impeachment proceedings, despite saying Sunday that the president “richly deserves” to be impeached.

Progressives argued following Mueller’s congressional testimony last week that while the special counsel’s performance was not rhetorically dazzling, he has already provided the House with more than enough evidence to move forward with an impeachment inquiry.