Currently, there are almost 150 federal district and appeals court vacancies around the country, a number that has risen from just over 100 when Mr. Trump took office, despite his notable success at filling openings. Democrats’ weakening of the filibuster against nominees in 2013 and a recent Republican decision to limit the veto power of home-state senators over judicial candidates have left few avenues to impede Mr. Trump and his Senate allies in their determination to fill judicial openings.
Last month, the president promised an intense push. “We’re going all out,” Mr. Trump told a cheering audience in Ohio, declaring that his ability to fill scores of open slots was a “gift from heaven,” as well as “world-changing, country-changing, U.S.A.-changing.”
Mr. Trump chastised the Ninth Circuit last year for its ruling against his travel ban, and for a district court judge’s move to block enforcement of a threat by his administration to withhold federal aid from so-called sanctuary cities. “Ridiculous rulings,” he railed on Twitter. “See you in the Supreme Court!”
Though analysts say it has become more moderate in recent years, the Ninth Circuit has long been the bane of conservatives, partly because of the influence of Judge Reinhardt and another Jimmy Carter-era appointee, Harry Pregerson, who died in 2017 after taking senior status in 2015.
It is the nation’s largest appeals court, covering nine Western states and dealing with a staggering set of topics from social questions like same-sex marriage to border issues to land resource matters. Because of its size, experts say that Mr. Trump would be unable to reverse its ideological makeup even if he were able to fill all eight vacancies. Some of those nominees would replace judges who had been appointed by other Republican presidents.
But there is no dispute that Mr. Trump has the chance to push it to the right. The dynamics of the court could change in many subtle ways — producing, for example, more sharp dissents that catch the attention of the Supreme Court, said Leonard Leo, the executive vice president of the Federalist Society.
Plus, it is hard to measure the effect of the loss of Judge Reinhardt, who was seen as a major influence on the liberal wing of the court and a talented and articulate legal protector of liberal views. “The death of Judge Reinhardt means more than the loss of a liberal vote,” said Arthur Hellman, a law professor at the University of Pittsburgh and a leading expert on the appeals court.
The mounting vacancies throw the future of the Ninth Circuit into the continuing Senate clash over the federal judiciary, one area where Mr. Trump has had success, with the enthusiastic assistance of Senator Mitch McConnell, the Kentucky Republican and majority leader. Since Mr. Trump took office, the Senate has confirmed not only Justice Neil M. Gorsuch of the Supreme Court, but also a record 14 appeals court judges and 14 district court judges.
Many more are in the pipeline. “I believe that’s the most important thing we are doing,” Mr. McConnell told a newspaper editorial board last week in Kentucky.
The Trump administration has already put forward two nominees for Ninth Circuit openings. One, Mark Bennett, the former attorney general of Hawaii, has the support of the state’s two Democratic senators.
But the other, Ryan Bounds, a federal prosecutor in Oregon, faces objections from the state’s two Democratic senators, setting up a showdown over that choice.
After Judge Reinhardt’s death created another California vacancy on the court, Senator Dianne Feinstein, the Californian who is also the senior Democrat on the Judiciary Committee, said she would resist efforts to remake a court that has been willing to defy the president.
“It’s no secret that President Trump and Republicans want to reshape the Ninth Circuit, and we will not accept unwarranted, partisan attacks on our courts,” she said in a statement. “I am fully committed to ensuring that Ninth Circuit nominees reflect our state’s communities and values and are well regarded by their local bench and bar.”
But she may find it hard to deliver on that guarantee. Senator Charles E. Grassley of Iowa, the Republican chairman of the Judiciary Committee, will probably proceed carefully, given his need to work cooperatively with Ms. Feinstein. But Mr. Grassley — with Mr. McConnell’s eager backing — has decreed that he will not allow home-state senators to use the so-called blue slip process to block appeals court nominees, as they have in the past.
The changes to the Ninth Circuit and the rest of the federal bench are now playing out with several questions looming, including how quickly the White House will act and how driven Senate Republicans will be to confirm judges before a November election that could change control of the Senate.
Some Republicans have threatened more rules changes if Democrats continue to slow-walk nominees.
One thing is certain, though — any Ninth Circuit nominee chosen by Mr. Trump will bear little resemblance to Judge Reinhardt.