Schumer sent a letter to Justice Department Inspector General Michael Horowitz on Tuesday saying the DOJ decision has "all the indicia of improper political interference in a criminal prosecution."

"The American people must have confidence that justice in this country is dispensed impartially. That confidence cannot be sustained if the president or his political appointees are permitted to interfere in prosecution and sentencing recommendations in order to protect their friends and associates," Schumer wrote.

The New York Democrat asked Horowitz to determine "how and why the Stone sentencing recommendations were countermanded, which Justice Department officials made this decision, and which White House officials were involved."

Schumer also requested Horowitz give an "expedited review" that ends with him publicly releasing his findings and recommendations "as soon as possible."

Democrats have seized on the Justice Department's decision to reduce the recommended sentence for Stone.

Schumer tweeted earlier Tuesday that he thought Horowitz "must open an investigation immediately." He said separately during a weekly press conference that he believes Stone should serve the initial seven to nine years recommended.

"The president seems to think the entire Justice Department is just his personal lawsuit to prosecute his enemies and help his friends. Rule of law in this grand, grand tradition, in this wonderful Justice Department is just being totally perverted to Donald Trump's own personal desires and needs, and it's a disgrace," he said.