Sen. Ben Sasse criticized President Donald Trump for threatening to challenge licenses of television networks, saying he had violated his oath of office to defend the Constitution.

The Nebraska Republican tweeted his response to Trump and posted a statement saying Trump was abdicating his constitutional duties.

“Are you recanting of the Oath you took on Jan. 20 to preserve, protect and defend the First Amendment?” the tweet read.

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’s statement came in response to Trump’s tweets on Wednesday, in which the president criticized NBC for a news story and asked, “at what point is it appropriate to challenge their License?”

With all of the Fake News coming out of NBC and the Networks, at what point is it appropriate to challenge their License? Bad for country!

— Donald J. Trump (@realDonaldTrump) October 11, 2017

Former Florida Gov. Jeb Bush, who ran against Trump in the presidential primaries, retweeted Sasse’s message.

But Sasse also had his critics, as Fox News host Sean Hannity, who interviewed Trump on Wednesday, called Sasse “just useless.”

One of the biggest mistakes in my career was supporting @BenSasse Just useless. https://t.co/bYReWFdfKO

— Sean Hannity (@seanhannity) October 12, 2017

Violating the oath of office is an impeachable offense, but Sasse gave no indication of any action he would take.

The Twitterverse called on the senator to do more than simply tweet his sentiments.

Brave tweet. Not as brave as Eminem. Actually do something other being “tough on Twitter.”

— Brian Johns (@BrianEJohns8790) October 12, 2017