WASHINGTON • Sen. Claire McCaskill said Thursday she is “very uncomfortable” with an anonymous editorial in the New York Times from inside the White House that is highly critical of President Donald Trump and calls into question his fitness for the office.

McCaskill, D-Mo., said that person should step forward for those allegations to be taken seriously, and she suggested that some Republican Senate colleagues are also hiding similar concerns about Trump.

Her remarks came during a call with reporters in which the president of the National Border Patrol Council, which supports Trump, announced that his employee union was endorsing McCaskill in Missouri’s pivotal United States Senate race.

The New York Times on Wednesday published an anonymous opinion piece from a self-described senior official in the White House who describes the president as unstable and says that members of the Cabinet briefly considered invoking the 25th Amendment, which lays out how a president can be removed from office by the vice president and members of the Cabinet.

Simultaneously, Bob Woodward’s new book, “Fear: Trump in the White House,” asserts that some in the White House believe Trump is “unhinged,” and that the president is on the verge of “nervous breakdown.”