Donald Trump announced this afternoon that he would nominate Robert F. Kennedy Jr. to lead the Department of Health and Human Services. Kennedy’s vaccine skepticism and unorthodox views about medicine make many public health officials deeply uneasy. Some Republican senators have suggested that his nomination gives them pause, but none ruled out voting to confirm him.

For years, Kennedy has battled the health agencies that he would oversee. He has spread false information about vaccines, including that they cause autism. And he has publicly contradicted the C.D.C.’s recommendation that communities fluoridate their water to guard against tooth decay.

Other cabinet picks, including Pete Hegseth, a Fox News host and Army veteran, as secretary of defense, and Tulsi Gabbard, a former Democratic congresswoman, as the director of national intelligence, have caused some Republicans to raise their eyebrows. But the nomination of Matt Gaetz to be attorney general has caused particular concern, and even disbelief.

Gaetz, a firebrand representative from Florida, was the focus of a federal investigation into sex-trafficking allegations. Lawmakers in both parties called today for a congressional panel to put out a highly critical report about Gaetz’s alleged misconduct that had been scheduled for release this week. “I don’t think he’s a serious candidate,” one senator said. Trump’s decision to nominate him came together over the course of a roughly two-hour flight.

Our congressional correspondent Catie Edmondson told me that House Republicans were “ebullient” after clinching control in the chamber and clearing the way for Trump to enact his agenda. “But over in the Senate, the Matt Gaetz nomination went over like a lead balloon.”

It’s not clear whether Gaetz will have enough support to be confirmed. But his nomination sent an unmistakable message to the nonpolitical career officials who form the backbone of federal law enforcement: Get in line or get out.