Advocates on the left expressed frustration Monday that President Barack Obama has not pushed harder to seat judges on the powerful federal appeals court in Washington.

Having withdrawn an embattled nominee for the bench last week, Obama remains the only president to serve a full four-year term without successfully nominating a judge to the Court of Appeals for the District of Columbia Circuit.

The appeals court is widely considered the second most-powerful court in the nation because of its near-exclusive jurisdiction over important national security and administrative law cases. But four of its 11 active judgeships are vacant — more as a percentage than any other circuit court — and its pending cases per judge has increased sharply in recent years. The seat vacated by U.S. Chief Justice John G. Roberts Jr. remains vacant nearly eight years after President George W. Bush elevated Roberts to the Supreme Court.

On March 22, Obama withdrew Caitlin J. Halligan from consideration after Republican senators successfully filibustered her nomination for a second time. The GOP characterized Halligan as an activist who might not share their view of the Second Amendment.

Obama criticized what he called the GOP’s “unjustified filibuster” of Halligan and said he is “committed to filling these vacancies to ensure equal and timely access to justice for all Americans.”

But some of Obama’s supporters are frustrated with his handling of nominations. During a panel discussion at the liberal Center for American Progress— which has close ties to the White House — Senate Republicans were blamed for blocking Halligan, but the president was taken to task for making too little effort to put judges on the D.C. Circuit.

“I have actually been totally baffled by why the White House is so behind on sending names up to the Hill on this,” said David Baron, managing attorney at the environmental advocacy group Earthjustice. The administration’s first-term record on the D.C. Circuit is “not just a missed opportunity, but a failure in responsibility because of the critical importance of this court,” he said. “They need to get on the dime now.”

Baron and Leslie M. Proll, director of the Washington office of the NAACP Legal Defense and Educational Fund, agreed that Bush placed much more emphasis on circuit court appointments.

Four months after taking office in 2001, Bush held an event in the White House Rose Garden to announce the nomination of 11 circuit court judges, Proll recalled. “It very much sent a signal that this president was going to make judicial nominations — and circuit court appointments, in particular — a very, very high priority,” she said.

Stephen I. Vladeck, an American University law professor, said “It’s right to point fingers in both directions on Pennsylvania Avenue.”

Vladeck said he was impressed that Obama renominated Halligan to the D.C. Circuit after her confirmation was blocked in 2011, calling that a sign of resolve on the part of the president. But he said the White House did not follow through with the kind of political pressure that could have led to Halligan’s confirmation. There was “very little sustained effort” by Obama to win confirmation of Halligan, Vladeck said.

Monday’s discussion focused largely on the importance of the D.C. Circuit, which Democrats say has become increasingly conservative and “out of the mainstream” in its rulings, as Caroline Fredrickson, president of the American Constitution Society for Law and Policy, put it.

Vladeck said that while the court now includes four judges appointed by Republican presidents and three appointed by Democrats, the Democratic appointees are more centrist than the Republicans. To call the court ideologically balanced is true “only at the most superficial level,” he said.

Fredrickson said administration officials “certainly understand the gravity of the situation,” and predicted that Obama will place more emphasis on the D.C. Circuit in the coming months.