It has opposed President Donald Trump's policy changes on asylum seekers, stood in the way of his travel ban and even blocked his effort to defund sanctuary cities.
The rulings, all by judges on the 9th Circuit Court of Appeals, have produced repeated presidential tongue-lashings.
Now, as the president continues his record-setting pace of filling vacancies on the federal bench -- something that will leave a lasting imprint on American jurisprudence for years to come -- Trump is poised to fill two vacant seats in California on the 9th Circuit Court, despite objections of the state's two Democratic senators.
Sens. Dianne Feinstein and Kamala Harris, who's seeking the Democratic presidential nomination, have voiced their repeated opposition to nominees Daniel Collins and Kenneth Lee. The two senators have attempted to withhold their approval, something that historically might have amounted to a senatorial veto.
But Senate Judiciary Committee Chairman Lindsey Graham, R-S.C., is moving forward with a confirmation hearing for both men on Wednesday, ignoring the fact that both senators failed to return what are called "blue slips."
The more-than-100-year-old Senate tradition allows a senator from that state to fill out a form -- printed on blue paper -- to indicate approval or opposition to a particular nominee. More often than not, the chairman of the Judiciary Committee -- regardless of party -- would insist on receiving the "blue slip" approval of a state's senators before proceeding with a confirmation hearing.
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Graham said he would work with Democrats to find "common ground" on lower court nominees, but that he would not "give a veto" to senators, regardless of party.
He has the considered support of Senate Majority Leader Mitch McConnell, R-Ky., who has called the confirmation of judges his "top priority." McConnell effectively changed the "blue slip" convention when Trump took office.
Al Drago/Getty ImagesPresident Donald Trump walks on the South Lawn of the White House, on March 10, 2019, in Washington after returning from Mar-a-Lago in Florida.
And Republicans are poised to go further as they look to change the Senate rules, with or without Democratic support, to dramatically reduce the amount of debate time lower court and executive nominees receive before final approval.
"We're still hoping to have bipartisan support to go forward with the standing order," McConnell has said of the coming rules change. "In the absence of that, it's still my desire to try to achieve that."
With the confirmation Tuesday of Paul Matey, former deputy chief counsel to former New Jersey Gov. Chris Christie, to be a judge on the 3rd Circuit Court, Trump has now appointed 35 jurists to the appeals bench and effectively flipped the 1st Circuit Court to a majority appointed by GOP presidents.
Sen. John Cornyn, R-Texas, when asked about the pace of confirmations, said, "It's one thing we can get done for sure that's going to last a long, long time."
But Democrats have blasted the moves.
"I know this is what my friend, the majority leader cares about -- a hard-right bench. He doesn't care about the qualifications. He doesn't care about moderation," Senate Minority Leader Chuck Schumer said Monday in a floor speech, adding, "He's running a conveyor belt of political partisans, many with extremely thin legal resumes."
Conservatives have long railed against the 9th circuit, seeing it as too liberal, but Trump has said so repeatedly, recently calling the court "a disgrace" after it opposed him on border security. The president even provoked Supreme Court Chief Justice John Roberts to speak out last year after he called a particular jurist on the federal court "an Obama judge," in the wake of a ruling related to asylum policy changes.
"Justice Roberts can say what he wants," Trump vented on Twitter at the time, "But the 9th Circuit is a complete & total disaster. It is out of control, has a horrible reputation, is overturned more than any Circuit in the Country, 79%, & is used to get an almost guaranteed result."