"Today is indeed a dark day for the United States of America. It is unconscionable for a President to indict the leading candidate opposing him," McCarthy said on Twitter.
"Joe Biden kept classified documents for decades. I, and every American who believes in the rule of law, stand with President Trump against this grave injustice. House Republicans will hold this brazen weaponization of power accountable."
McCarthy's remarked reiterated similar sentiments aired by Florida Governor Ron DeSantis, who blasted the "weaponization of federal law enforcement agencies" as a "mortal threat to a free society."
"We have for years witnessed an uneven application of the law depending upon political affiliation," he continued, claiming that a DeSantis White House would "excise political bias and end weaponization once and for all."
Earlier Thursday, Trump revealed on Truth Social that "the corrupt Biden administration" had informed his lawyers that he had been indicted in a federal investigation over alleged mishandling of classified documents at his Florida residency, and was summoned to appear in court on Tuesday.
The ex-president expressed despair over the indictment, pointing out that he is being prosecuted as polls show he is by far the leading candidate among both Republicans and Democrats.
US media reported on Thursday that Trump is facing seven counts that include willful retention of national defense information, corruptly concealing docs, conspiracy to obstruct justice, and false statements.
Trump has denied any wrongdoing in the classified documents case and the other three criminal probes he is involved in, including charges of falsifying business records and the former president's alleged involvement in the events on Capitol Hill on January 6, 2021.