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Sen. Kamala Harris is accusing President Trump of using his judicial appointments to weaken the rights of groups such as immigrants and transgender soldiers, and says she will vote against all of his nominees to the federal courts.

“This administration is packing the court that protected Dreamers from deportation and blocked the unconstitutional transgender military ban,” Harris, D-Calif., said in a tweet last week, just days after announcing her candidacy for president in 2020.

“We need nominees who will uphold equality and justice,” she said. “Until a fair process is in place, I will oppose every nominee to an appellate court.”

The court she accused the administration of packing is the Ninth U.S. Circuit Court of Appeals in San Francisco, a favorite target for criticism from the political right. Trump has regularly denounced that court as “disgraceful” for its rulings against him, including one blocking his plan to deport 700,000 undocumented immigrants — called “Dreamers” by their supporters — who were brought to the United States or arrived on their own before their 16th birthday.

The appeals court also refused last July to let Trump implement a ban on transgender service in the military. The president has issued a revised order that would exclude most transgender troops, and the Supreme Court has signaled that the order will be allowed to take effect while it is being challenged in lower federal courts, including the Ninth Circuit.

Harris has voted for some of Trump’s judicial nominees, but only one of two of his picks for the Ninth Circuit. Mark Bennett, a former Republican state attorney general in Hawaii, was confirmed to the Ninth Circuit in July with the help of Harris’ vote, but over the opposition of more than half the Senate’s Republicans because of his past support of gun control.

She did not support Trump’s other current Ninth Circuit appointee, Ryan Nelson, who was confirmed in October on a party-line vote. The court remains one of the nation’s more liberal circuits, with 16 judges appointed by Democratic presidents and seven by Republicans. The court has six vacancies.

But Harris and California’s other Democratic senator, Dianne Feinstein, have protested Trump’s latest selections for three Ninth Circuit seats formerly held by Californians, nominations on which California senators have usually been consulted in the past.

The prospective nominees are Kenneth Lee, a Los Angeles attorney who served in the White House counsel’s office under President George W. Bush; Daniel Collins, another Los Angeles attorney who was an official in the Bush Justice Department; and Daniel Bress, a Washington, D.C., lawyer and onetime law clerk to Supreme Court Justice Antonin Scalia.

The senators said they were prepared to negotiate with the White House to fill the vacancies, a common practice in the past when a nominee’s home-state senators are from a different party than the president. But the Republican chairman of the Senate Judiciary Committee, Lindsey Graham of South Carolina and his predecessor, Charles Grassley of Iowa, have abolished the practice of giving senators a veto — known as a blue slip — over appeals court candidates in their state. Both Harris and Feinstein are committee members.

“We’ve shown that we’re willing to work with the White House” on candidates for U.S. District Court, where the blue-slip process remains in effect, Harris and Feinstein said in a joint statement. They also said all three Ninth Circuit candidates have no judicial experience and that Lee had failed to turn over “controversial writings” to the senators’ judicial selection committees, Collins was known for trying to “push legal boundaries,” and Bress was not a Californian.

Harris’ stance is both good policy and good politics, said Jessica Levinson, a law professor at Loyola Law School in Los Angeles who specializes in election and governance issues.

“The rejection of the blue slips was particularly egregious” because it eliminates the powers of home-state senators from minority parties, Levinson said.

She said Harris was also sending a message to prospective voters that “I’m the person who’s going to stand up to Donald Trump, and use all the power I have at my disposal.”

Bob Egelko is a San Francisco Chronicle staff writer. Email: begelko@sfchronicle.com

Twitter: @BobEgelko