Ben Sasse is not OK with Donald Trump’s tweets. On June 29, the president began yet another day by barfing out insults on Twitter, this time regarding MSNBC host Mika Brzezinski’s face. Sasse was one of the first Republicans to respond. “Please just stop,” wrote Nebraska’s 45-year-old junior senator. “This isn’t normal and it’s beneath the dignity of your office.”

Dignity is one of Ben Sasse’s things. He’s also into duty, thoughtfulness, empiricism, and respect for democratic traditions—and while most politicians would probably claim to support those ideals, Sasse sets himself apart by frequently challenging his party on their behalf. The Morning Joe incident was not nearly the first time Sasse has criticized Trump without rationalizing or minimizing his behavior the way so many in the GOP do; during the 2016 presidential campaign, Sasse refused to endorse the real estate heir even as almost all of his Republican peers in elected office folded. (He called for an independent candidate to run against Trump and Clinton in a widely discussed Facebook post but reportedly rebuffed suggestions by Mitt Romney and Bill Kristol that he become that candidate himself.) Just this Sunday, Sasse called Trump’s claim to be working on a cybersecurity commission with Vladimir Putin “bizarre” and noted (correctly) that it “should obviously not happen.”

In a world of phonies, Sasse stands out by educating himself earnestly and speaking honestly about complicated matters of history and policy.