Senate Majority Leader Mitch McConnell on Wednesday rejected legislation from Sen. Jeff Flake aimed at protecting special counsel Robert Mueller from being fired by President Trump.

Flake, R-Ariz., and several other senators are worried that Trump’s decision to fire Attorney General Jeff Sessions is a sign Trump might soon try to move against Mueller, who is investigating Trump’s alleged ties to Russia during the 2016 election. Trump’s new acting attorney general, Matthew Whitaker, has also said previously he’s opposed to the Mueller investigation, which has raised more fears that Mueller’s work could be stopped.