Sen. Adam B. Schiff on Monday rebuffed as a baseless threat a weekend broadside from President Trump in which Trump alleged that Schiff and others could still face investigation for actions covered by a slate of late pardons issued by President Biden.

“Your threats will not intimidate us,” the California Democrat wrote on X. “Or silence us.”

Schiff, elected last year to fill the Senate seat long held by the late Sen. Dianne Feinstein, is among those who received a pardon from Biden in the final days of his presidency, despite having personally discouraged the move.

Schiff previously served in the House, where he helped lead the select committee to investigate the Jan. 6, 2021, attack on the U.S. Capitol by Trump’s supporters. The committee’s work led to Trump being impeached by the House — for a second time — for inciting the insurrection, which was an attempt to block the transfer of power to Biden.

Before leaving office, Biden issued a burst of pardons that he said were designed to protect individuals who had done nothing wrong but who could nonetheless be targeted for retribution by Trump. That included the members of the select committee, including Schiff, one of Trump’s most vociferous critics.

Trump has lambasted Biden’s pardons since they were issued. But he went a step further in a Sunday post on his social media platform Truth Social, in which he adopted a conspiracy theory pushed online by right-wing pundits that Biden’s pardons were invalid because they were signed using an “autopen” — resulting in a digital, not handwritten, signature.

The theory ignores the fact that digital signatures are commonly used across government and have been accepted for years, that other presidents have used autopens to sign important measures and pardons, and that the Justice Department’s Office of Legal Counsel under President George W. Bush issued a memorandum opinion justifying their use in 2005.

The theory also plays on the notion that Biden, now 82, was mentally absent or overly reliant on aides toward the end of his term. Elon Musk, Trump’s broadly empowered government efficiency advisor and the world’s richest man, posted on Sunday afternoon an image showing a line of presidential portraits, with Biden’s replaced with the image of an autopen.

Hours later, Trump — who edged out Biden as the oldest president ever to be inaugurated in January — posted his remarks on Truth Social.

“The ‘Pardons’ that Sleepy Joe Biden gave to the Unselect Committee of Political Thugs, and many others, are hereby declared VOID, VACANT, AND OF NO FURTHER FORCE OR EFFECT, because of the fact that they were done by Autopen,” Trump wrote. “In other words, Joe Biden did not sign them but, more importantly, he did not know anything about them!”

Trump also repeated claims he has previously made that the select committee deleted evidence in its “witch hunt” against him, and said its members “should fully understand that they are subject to investigation at the highest level.”

Trump’s remarks were the latest indication that he intends to target Democrats for political retribution despite his repeated promises that his administration would bring an end to the political “weaponization” of the justice system. Trump has installed loyalists who backed his lie that the 2020 election was stolen from him at the highest levels of the Justice Department, increasing concerns that politically motivated investigations could be launched.

Schiff said the members of the Jan. 6 committee “are all proud of our work.”

Rep. Bennie G. Thompson, a Mississippi Democrat and chair of the Jan. 6 committee, echoed Schiff.

“Trump was responsible for Jan 6. That’s why on day one he pardoned those who beat police that day,” Thompson wrote on X, referring to Trump’s decision to pardon or grant clemency to those criminally charged in the insurrection.

“We thoroughly & legally investigated what he did and have lived rent free in his mind since. He knows his guilt,” Thompson said. “I am not afraid of his rant that has no basis in reality.”