Oklahoma Republican Sen. James Lankford said Thursday he believed Federal Reserve Chair Jerome Powell couldn’t be fired by President Donald Trump.

“No, I don’t think he’s going to be fired or that he could be at that point,” Lankford told Semafor World Economy. Trump has pressured Powell to lower interest rates and has threatened to fire Powell if he didn’t depart from the job. US Attorney Jeanine Pirro has spearheaded an investigation into Fed renovations during Powell’s tenure, frustrating some GOP senators, one of whom has vowed to block Trump’s new Fed nominee Kevin Warsh until the investigation was dropped.

But Lankford was confident the Pirro-led investigation would soon be wrapped up.

“I think the investigation will come to a conclusion in the next couple weeks,” he said.

Despite Trump’s repeated calls for senators to kill the filibuster, Lankford said, “I do not think we should kill the filibuster.”

“It literally forces one place in government where both sides have to be grown ups and talk to each other,” he added.

Lankford also said Senate Republicans had work to do between now and midterm elections in November to keep their majority. Running on the tax cuts passed last year might not be enough, he said, quipping that “elections are in November, taxes are in April.”

“I don’t think people are thinking about taxes once they get to November. They’re thinking about it now and thinking maybe it’s better. But we’ve still got to be able to show our work for the rest of the year.”