(CNN) House Speaker Nancy Pelosi on Saturday slammed President Donald Trump's decision to commute the prison sentence of his long-time friend and political adviser Roger Stone as "an act of staggering corruption."
"President Trump's decision to commute the sentence of top campaign advisor Roger Stone, who could directly implicate him in criminal misconduct, is an act of staggering corruption," Pelosi said in a statement.
Pelosi said that Congress will take action to "prevent this type of brazen wrongdoing" and that legislation is needed to "ensure that no President can pardon or commute the sentence of an individual who is engaged in a cover-up campaign to shield that President from criminal prosecution."
The President has broad constitutional power to pardon and grant clemency, and Friday night the White House announced that Trump commuted Stone's sentence days before he was set to report to a federal prison in Georgia.
Before the White House's announcement late Friday, Pelosi told CNN's Anderson Cooper that granting clemency for Stone is "appalling" and "ridiculous."
Stone was convicted in November of seven charges, which included lying to Congress and witness tampering, as part of former special counsel Robert Mueller's Russia investigation. Among the things he misled Congress about were his communications with Trump campaign officials, which prosecutors said Stone hid out of his desire to protect the President.
Trump's move spares Stone from having to serve jail time after a judge sentenced him in February to 40 months in prison -- but the guilty verdicts remain on the books.
The President defended his decision in his first public comments on the matter Saturday.
"Roger Stone was targeted by an illegal Witch Hunt that never should have taken place. It is the other side that are criminals, including Biden and Obama, who spied on my campaign - AND GOT CAUGHT!" the President wrote on Twitter.
Trump nor his allies have offered any proof that former President Barack Obama or former Vice President Joe Biden had "spied on" Trump's 2016 campaign.
The President appeared to be referring to court-authorized wiretaps of former Trump campaign official Carter Page -- after he had left the campaign -- although the Justice Department later said it had "insufficient" reason to continue the wiretaps.
House Intelligence Committee Chairman Adam Schiff told NBC News on Saturday that by granting clemency to Stone, Trump is sending the message "if you lie for the President, if you cover up for the President, if you withhold incriminating evidence for the President, you get a pass from Donald Trump."
Schiff, a Democrat, argued that such actions establish two standards of justice in the United States -- one for Trump's "criminal cronies" and another for everyone else.
He argued that legislation to curb future abuses needs to be passed, pointing to a bill he introduced in March 2019.
Schiff's bill, the "Abuse of the Pardon Prevention Act," would require any evidence be provided to Congress if a president grants clemency to an individual tied to an investigation in which the president or a family member is a witness, subject, or target.
The bill was introduced amid Schiff's concerns that Trump would "undermine" former special counsel Robert Mueller's investigation by using his pardon powers and before Trump's former campaign manager Paul Manafort was scheduled to be sentenced.
Mueller, in a Washington Post op-ed Saturday, defended Stone's prosecution, writing, "Stone was prosecuted and convicted because he committed federal crimes. He remains a convicted felon, and rightly so."
Mueller went on to note in the piece, "Because his sentence has been commuted, he will not go to prison. But his conviction stands."
"We made every decision in Stone's case, as in all our cases, based solely on the facts and the law and in accordance with the rule of law. The women and men who conducted these investigations and prosecutions acted with the highest integrity. Claims to the contrary are false," Mueller wrote.
As Democratic leadership on Saturday condemned the President's act of clemency for his friend, most Republican lawmakers have so far remained quiet on the matter.
Senate Majority Leader Mitch McConnell's office had no comment on Stone's commutation. And a spokesman for House Minority Leader Kevin McCarthy hasn't responded to a request for comment.
GOP Sen. Mitt Romney, however, swiftly condemned the President's move as "unprecedented, historic corruption."
"Unprecedented, historic corruption: an American president commutes the sentence of a person convicted by a jury of lying to shield that very president," the Utah Republican said on Twitter Saturday.
White House press secretary Kayleigh McEnany responded to Romney's comments on Saturday, saying in part that "the only 'unprecedented, historic corruption' that occurred was during the Obama-Biden administration." McEnany, in her Saturday response, also repeated some of the false claims the White House made Friday in a lengthy statement following the commutation.
Stone also responded to Romney on Saturday. In a video posted to Twitter, Stone insulted Romney and said the senator did not have the "facts" about his case "correct."
Once the party's standard bearer and presidential nominee, Romney is often one of the GOP's only members voicing opposition to some of Trump's actions.
Romney was the sole Republican senator earlier this year to break with his party and vote to convict Trump on one of the articles of impeachment against the President, abuse of power. The Senate ultimately voted to acquit Trump on two articles of impeachment, finding he was not guilty of abuse of power and obstruction of Congress.
Later on Saturday, another Republican, Sen. Pat Toomey of Pennsylvania, called Trump's decision to commute Stone's sentence a "mistake" and said that the president's power to grant clemency for federal crimes "should be used judiciously and very rarely."
"While I understand the frustration with the badly flawed Russia-collusion investigation, in my view, commuting Roger Stone's sentence is a mistake," Toomey said in a statement. "He was duly convicted of lying to Congress, witness tampering, and obstructing a congressional investigation conducted by a Republican-led committee."
This story has been updated to include reaction from former special counsel Robert Mueller, comments from Sen. Mitt Romney, the White House's reaction to them, a statement from Sen. Pat Toomey and comments from Roger Stone responding to Romney.