WASHINGTON — In 2011, Michael B. Brennan, then a lawyer in Milwaukee, vigorously defended the right of Wisconsin’s Republican senator to single-handedly block an Obama administration nominee for a federal bench seat in the state. Last week, Mr. Brennan was confirmed as a Trump administration nominee to that very same seat despite vigorous objections by the state’s Democratic senator.

That incongruity is at the heart of what is fast becoming one of the most significant questions on Capitol Hill: How far will Republican senators go in pushing through President Trump’s judicial nominees over the objections of Democrats from states where the potential new judges will preside?

The answer: pretty far.

Mr. Brennan was the second federal appellate court nominee confirmed despite a refusal by one home-state Democrat to consent to the nomination through the longstanding Senate tradition of signing and returning a blue-tinted form — known universally as the blue slip — demonstrating acquiescence in the presidential appointment.

Now the Senate Judiciary Committee could send to the floor a disputed nominee from Oregon who is opposed by both of that state’s senators, a major break with Senate custom. According to the Congressional Research Service, it would be the first time since at least 1979 that a federal judge could be confirmed over the objections of both home-state senators. Democrats believe it could be the first time ever.