WASHINGTON — The doors to the Republican cloakroom off the Senate floor swung open and out walked Senator Ron Wyden, an Oregon Democrat who is not usually found in the inner sanctum of the majority party.

He had been buttonholing Republican colleagues, trying to persuade them that racially charged college writings by Ryan W. Bounds, a federal appeals court nominee from Mr. Wyden’s home state, were disqualifying and that he should be rejected. His crusade seemed unlikely to succeed, given that disciplined Senate Republicans have been pushing through Trump administration judicial picks with assembly-line efficiency over the heated complaints of Democrats.

But in a stunning development, the nomination of Mr. Bounds was withdrawn at the last minute on Thursday because of Republican objections, a sharp turn of events with significant implications for both the Senate and the coming showdown over the nomination of Judge Brett M. Kavanaugh to the Supreme Court.

“Today, the Senate came to its senses with respect to judges,” said Mr. Wyden, who teamed up with his home-state Democratic colleague, Jeff Merkley, to try to educate Republicans about Mr. Bounds’s writings from his time at Stanford. (Democrats cited numerous articles they considered racist, inflammatory and offensive, and also said Mr. Bounds had not been forthright about producing them.)