A Republican senator is openly questioning Donald Trump’s commitment to defending the Constitution after the president’s latest attacks on the media.

Trump on Wednesday tweeted:

Network news has become so partisan, distorted and fake that licenses must be challenged and, if appropriate, revoked. Not fair to public! — Donald J. Trump (@realDonaldTrump) October 12, 2017

Earlier in the day, he launched a similar attack on NBC News.

Sen. Ben Sasse (R-Neb.) fired back late Wednesday with a statement asking Trump if he is recanting the oath to “preserve, protect and defend the First Amendment.”

He wrote:

Mr. President:

Are you recanting of the Oath you took on Jan. 20 to preserve, protect, and defend the 1st Amendment? pic.twitter.com/XLB7QXM3bQ — Ben Sasse (@BenSasse) October 12, 2017

Sasse has been a frequent Trump critic, and over the summer he called on him to stop the Twitter feuds.

“Please just stop,” he wrote on the social network. “This isn’t normal and it’s beneath the dignity of your office.”