As he helped speed Judge Brett M. Kavanaugh’s embattled nomination toward a vote this week, Senator Charles E. Grassley of Iowa, the Republican chairman of the Judiciary Committee, declared that the Senate was approaching “rock bottom” and needed to right itself.

Mr. Grassley, 85 and a senator for nearly four decades, said it was time for “mending things so we can do things in a collegial way, that the United States Senate ought to do.”

That sentiment, from a lawmaker who fiercely defended Judge Kavanaugh and helped block President Obama’s nominee to the Supreme Court, Judge Merrick B. Garland, drew skepticism or scorn from many in the political world. It also felt like a glaring understatement: Brute partisanship in the Senate is a symptom of a much larger national contagion.

To the right and left alike, Judge Kavanaugh’s nomination appears less like a final spasm of division — a sobering trauma, followed by calm resolution — than an event that deepens the national mood of turbulence. The country is gripped by a climate of division and distrust rivaled by few other moments in the recent past.