U.S. Sen. Cory Booker is calling for further action on his bill to prevent President Donald Trump from firing special counsel Robert Mueller.

Mueller is investigating possible collusion between the Trump campaign and Russia for possibly interfering the 2016 election.

The New York Times reported this week that Trump sought to fire Mueller last June, but backed off.

Booker’s bipartisan bill would provide a check on the power of the Executive Branch. The bill would allow judicial review of any decision to terminate a special counsel.

“It was a pragmatic imperative but now, given what we know, there's now a moral urgency for us to get this bill done,” Booker says. “So my cross-the-aisle work to get to this point now takes on more of an imperative.”

The president denies New York Times report that he planned to fire Mueller.