Comey’s attacks on Trump may hurt a carefully cultivated image

The personal potshots in particular have surprised some former colleagues who thought of Mr. Comey as relatively sober and serious. Observers on both the left and right — including many who count themselves as fierce critics of Mr. Trump’s — say that in embarking on his star turn, Mr. Comey may be undercutting his own indictment of the president’s character and conduct.

“The real impact of having the former head of the F.B.I. calling the president unfit is dependent on the just-the-facts professional image of the F.B.I.,” said Michael Steel, a Republican strategist who has been critical of Mr. Trump. “To the extent that the former director appears petty and anything less than high-minded, it diminishes the impact of his critique.”

“In a time when almost every public debate is defined by people lining up with their respective tribes,” Mr. Steel added, “he’s managed to alienate both.”