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.