WASHINGTON, DC - FEBRUARY 12: U.S. Sen. Chuck Grassley (R-IA) waits for the beginning of a news conference on immigration February 12, 2018 at the Capitol in Washington, DC. (Alex Wong/Getty Images)

The top Republican on the Senate Judiciary Committee is “incensed” at Attorney General Jeff Sessions for trying to derail a bipartisan bill that would reduce mandatory prison terms for drug offenders on the eve of its first procedural vote.

Sessions and Judiciary Chairman Charles E. Grassley (R-Iowa) have long been at odds over the bill, which would reduce the length of mandatory minimum sentences for repeat nonviolent drug offenses, eliminate the “three strike” provision that requires a life sentence, and give judges expanded authority to issue shorter-than-mandatory minimum sentences for low-level crimes. The changes, championed by Grassley, fly in the face of Sessions’s bid to wage a new war on drugs from the Justice Department — something he made clear in a letter to Grassley Wednesday, writing that passing the bill would be a “grave error.”

Grassley retorted publicly via Twitter, giving Sessions a piece of his mind and a short reminder about who in the government makes the federal laws — and who is supposed to follow them.

“Incensed by Sessions letter An attempt to undermine Grassley/Durbin/Lee BIPARTISAN criminal just reforms,” Grassley wrote. “This bill deserves thoughtful consideration b4 my cmte. AGs execute laws CONGRESS WRITES THEM!”

The Grassley-Session dispute over sentencing reform began long before Sessions joined the administration, to when both served on the Senate Judiciary Committee. Two years ago, Grassley joined with Sen. Richard J. Durbin (D-Ill.) on a previous iteration of the bill that collected 37 co-sponsors — but Senate Majority Leader Mitch McConnell (R-Ky.) never put it on the floor, under pressure from senators like Sessions not to.

Grassley and Durbin released the current version of their sentencing reform legislation in October, securing several high-profile endorsements from across the political and social spectrum — including the National Football League, the National Association for the Advancement of Colored People, the American Civil Liberties Union, the Charles Koch Institute, and Americans for Tax Reform. They invited input from the administration — but that came from periodic check-ins with President Trump’s son-in-law and senior adviser Jared Kushner, not Sessions.

In his letter to Grassley on Wednesday, Sessions again warned of the “potential ramifications” of the legislation, criticizing provisions that would reduce sentences and warning repeatedly, that it would complicate efforts to beat back gangs “like MS-13.” Trump has repeatedly referenced initiatives against MS-13, a gang with ties to El Salvador, to show that his administration was tough on crime and to bolster his case for a tough stance on immigration policy.

“This legislation would reduce sentences for a highly dangerous cohort of criminals, including repeat dangerous drug traffickers and those who use firearms, and would apply retroactively to many dangerous felons, regardless of citizenship or immigration status,” Sessions wrote in his letter to Grassley.

The legislation is not an across-the-board reduction in federal sentences; it also increases mandatory minimums for domestic abusers who cross state lines, people who export arms to terrorist groups and blacklisted countries, and people who traffic or deal fentanyl, a synthetic opioid that is far more potent and deadly than heroin.

Grassley is unfazed by the attorney general’s warnings. The Judiciary Committee is scheduled to vote Thursday morning on the sentencing reform legislation. It is expected to pass.