Rep. Ben Ray Luján (D-NM), the fourth-highest ranking House Democrat, announced his support Monday for an impeachment inquiry into President Donald Trump.

Luján cited the findings in former special counsel Robert Mueller’s report into now-debunked collusion between the 2016 Trump campaign and Russia as his chief motivation for supporting proceedings to oust the president, saying in a statement that his newly-announced position was not one he reached “lightly.”

“The report detailed sustained and frequent attempts by the Trump campaign to establish ties to the Russian government and an eagerness to benefit from hacked information stolen from our fellow Americans,” said the Assistant House Speaker. “The Special Counsel also detailed ten different attempts by President Trump to obstruct justice during the investigation. This would be unacceptable behavior from any president.”

“What is evident is that President Trump is abdicating his responsibility to defend our nation from Russian attacks and is putting his own personal and political interests ahead of the American people,” he added.

Luján’s support for impeachment makes him the highest-ranking House Democrat to back the measure and the 127th congressional Democrat to do so, according to Politico.

“Luján is the third member of House leadership to support the move, joining Reps. Katherine Clark (D-Mass.), the vice chair of the Democratic Caucus, and Rep. David Cicilline, head of the Democratic messaging arm,” the publication notes.

Luján’s support comes after the House Judiciary Committee announced the launch of its so-called “impeachment investigation.”

Appearing last month on ABC’s This Week, Judiciary Committee chairman Rep. Jerry Nadler (D-NY) explained his panel is “investigating whether to approve articles of Impeachment before the committee.”

“We have impeachment resolutions before the committee. We are conducting investigations to determine whether we should report those impeachment resolutions to the House or whether we should draft our own and report them to the House,” Nadler said.

“We’re considering those resolutions. we’ll make a determination after we get more evidence as to the president’s crimes that we had from the Mueller report and also from other things, violations of the emoluments clause, his failure to defend the constitution against repeated Russian attacks,” he added. “We’re investigating whether to approve articles of Impeachment before the Committee.”

Despite a growing number of House Democrats backing impeachment, House Speaker Nancy Pelosi (D-CA) has remained opposed to the move.

“We will proceed when we have what we need to proceed — not one day sooner,” Pelosi told reporters when asked about removing the president in July.

“Everybody has the liberty and the luxury to espouse their own position and to criticize me for trying to go down the path in the most determined, positive way,” the California Democrat added. “Again, their advocacy for impeachment only gives me leverage.”

Last month, the House voted 332-95 to table a measure that would begin an impeachment inquiry.