The one roadblock to criminal justice reform: Mitch McConnell

A new reform of the criminal justice system has attracted widespread bipartisan support, including conservative GOP Senators Mike Lee and Chuck Grassley.
President Trump, at the urging of his daughter and son-in-law Ivanka and Jared Kushner, also came out in support of the bill.
But the one stumbling block? Mitch McConnell. So far, he’s not committing to bring the bill to the floor, which basically kills the legislation’s prospects.
Breitbart reported on Sen. Lindsey Graham’s frustration with McConnell:

“I’m urging Mitch McConnell, put this bill on the floor. If you put it on the floor, we’ll get 80 votes. We’ll get most Republicans and almost all Democrats. Let’s do it before the end of the year, and the president is behind it. So Mr. president, pick up the phone and call the Republican leadership of the House and the Senate and say we still run this place. Bring this bill to the floor. Senator Cotton can have his say, and we’ll vote him down.”

We’ve criticized McConnell in the past as a globalist turtle and he’s giving us even more to critique. Why is he blocking a bill his president supports? This bill is grounded in conservative principles and will trim government spending. What gives?