Judge Brett M. Kavanaugh is sworn in during his Senate Judiciary Committee confirmation hearing on Sept. 4 in Washington. (SAUL LOEB/AFP/Getty Images)

The White House on Sunday stood by Brett M. Kavanaugh after a woman publicly accused him of sexual assault decades ago, an allegation that triggered the most concrete signs yet of Republican resistance to President Trump’s Supreme Court nominee.

With the nomination suddenly in doubt, Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa) was working to arrange follow-up calls with Kavanaugh and Christine Blasey Ford, the woman who said he assaulted her when the two were in high school.