President Trump and his conservative allies now see their effort to confirm Judge Brett M. Kavanaugh as central to salvaging the Republican Party’s fortunes in the midterm elections, and hope to use the fervent liberal opposition to his nomination to the Supreme Court as a graphic example of the threat posed by a Democratic return to power in Congress.

The increasingly aggressive attacks on Judge Kavanaugh’s main accuser and the dark warnings about Democrats from his supporters are part of an effort to harness Republicans’ outrage over what they see as a Democratic scheme to steal a pivotal Supreme Court seat.

“What the Kavanaugh controversy has done is increase Republican voting intensity so that it is approaching Democratic intensity, which is already through the roof,” said Whit Ayres, a Republican pollster. “Republicans perceive that Judge Kavanaugh is a man who has led an upright and honorable life, certainly as an adult, and feel like his reputation is being trashed and his nomination is being railroaded.”