The Office of the Director of National Intelligence on Friday issued the latest in a series of reports from the Trump administration attempting to undermine the eight-year-old assessment that Russia favored the election of Donald J. Trump in 2016.

Tulsi Gabbard, the director of national intelligence, said the information she was releasing showed a “treasonous conspiracy in 2016” by top Obama administration officials to harm Mr. Trump.

Democrats denounced the effort as politically motivated, error-ridden and in contradiction with previous reviews of the assessment.

Representative Jim Himes of Connecticut, the top Democrat on the House Intelligence Committee, called Ms. Gabbard’s accusation of treason “baseless.”