A Republican-led effort to overhaul the nation’s criminal justice system is being put on hold ahead of the midterm elections over fears it could be politically “problematic.”

Republicans have made a hardline approach to immigration and crime a cornerstone of their 2018 election message.

The White House and Senate Majority Leader Mitch McConnell agreed Thursday to pause a push for criminal justice reform legislation in the Senate until after the midterms, according to a senior White House official.

The initiative, which has been championed by the president’s son-in-law and adviser Jared Kushner, aims to reduce recidivism by expanding education for federal prisoners and requiring them to be placed in facilities closer to home, among other provisions.

The House passed a version of the bill in May with support from Trump and Attorney General Jeff Sessions.

(MORE: White House one step closer to a bipartisan victory with prison reform bill advancement)

In recent weeks, sources say, the president has also warmed to the idea of including broad sentencing reforms in the Senate version –- such as reducing mandatory sentences for nonviolent drug offenses -- a top priority of Iowa Sen. Chuck Grassley, who chairs the powerful Senate Judiciary Committee, and fiercely opposed by Sessions.

While the senior White House official said Trump is "positively inclined" to support some of the revisions that Grassley champions, he has not yet given his endorsement of a sentencing overhaul, and wants to continue the conversations, sources say.

(MORE: Trump has privately expressed openness to broad criminal justice reform)

“The President remains committed to meaningful prison reform and will continue working with the Senate on their proposed additions to the bill. The administration remains focused on reducing crime, keeping communities safe and saving taxpayer dollars," White House deputy press secretary Hogan Gidley said in a statement.

At a White House meeting Thursday with Sessions and Kushner, the president expressed particular opposition to reducing minimum sentences for opioid traffickers -- one official familiar with the conversation saying he even renewed calls for the death penalty for fentanyl traffickers. Gidley did not immediately respond to questions about the president's death penalty proposal.

(MORE: Inside Jared Kushner's personal crusade to reform America's prisons)

An administration official, speaking on condition of anonymity to describe the president's meeting with Sessions, said it was agreed today by attendees that approving any prison system or sentencing reforms ahead of the midterms could be “too problematic.”

The proposals have also been criticized by some Democrats and civil rights groups who argue that they do not go far enough in reforming the justice system and in reducing the size of the prison population.

The senior White House official said that ultimately it was McConnell's firm opposition to taking up the matter ahead of the elections that put the proposal on hold. A spokesman for McConnell would offer no comment on the meeting but did not dispute the account.

The Department of Justice sought to characterize the delay as a victory for the attorney general who remains opposed to any overhaul of tough mandatory sentences for drug offenders.

"We are pleased the president agreed that we shouldn't support criminal justice reform that would reduce sentences, put drug traffickers back on our streets and undermine our law enforcement officers who are working night and day to reduce violent crime and drug trafficking in the middle of an opioid crisis," said DOJ spokeswoman Sarah Isgur Flores.

Late Thursday, Grassley issued a statement praising Trump.

“I’m very encouraged by the leadership shown today by President Trump to make prison and sentencing reform a priority soon after the election and Leader McConnell’s openness to bring it up this year. And I’m confident with the President’s continued backing, we’ll have more than enough votes to pass a bill overwhelmingly," he said.

ABC News' Devin Dwyer contributed to this report.