Senate Republicans have declined to hold hearings for President Obama’s Supreme Court nominee, Merrick D. Garland. Garland currently is chief judge of the U.S. Court of Appeals for the D. C. Circuit. (Evan Vucci/AP)

An exodus of older judges has created a spike in vacancies at federal trial courts nationwide, intensifying complaints that election-year fights over ideological control of the bench now extend to lower-court appointments.

While Senate battles over nominees to the Supreme Court and appeals courts draw more headlines, the less-noticed openings are increasing workloads and delaying trials in federal courts that take in hundreds of thousands of cases a year — compared with the 80 or so cases heard by the nation’s highest court.

Of 673 U.S. district court judgeships, 67 — or 10 percent — are vacant under President Obama, nearly twice as many as at this point of Republican George W. Bush’s presidency and 50 percent higher than at this time under Bill Clinton (D) or George H.W. Bush (R), according to data kept by the Administrative Office of the U.S. Courts.

The number of federally designated district court “judicial emergencies” — where seats carry particularly heavy caseloads or have been open for an extended period — is also roughly double what it was in May 2008 and May 2000, according to the administrative office.

Heavy caseloads in some places slow resolution of everything from commercial disputes to workplace discrimination claims to federal regulatory challenges, in which district court rulings are often the last word because most are not appealed.

Because of the logjam in filling vacancies, some courts slog at less than full strength for years before getting a surge of new judges appointed by a single president. The feast-or-famine effect, as some legal analysts view it, has occurred in some of the busiest courts in the country and in jurisdictions as diverse as Texas and the District.

Chief Justice John G. Roberts decried the “persistent problem of judicial vacancies in critically overworked districts” in a 2010 year-end report, blaming both sides for creating “extraordinary caseloads.”

“Each political party has found it easy to turn on a dime from decrying to defending the blocking of judicial nominations, depending on their changing political fortunes,” Roberts said.

Since that warning, the problem has, by several measures, grown worse.

Recently retired Manhattan federal judge Shira A. Scheindlin, a 1994 Clinton appointee, called the failure to fill dozens of openings a “judicial scandal” ranking alongside the GOP-led Senate’s refusal to hold confirmation hearings for Merrick B. Garland, Obama’s election-year nominee to the Supreme Court.

“Obstructionism” undermines public trust in the courts, where at the trial level only experience and competence, not ideology, should count, Scheindlin wrote in a recent op-ed piece for the New York Times.

“Supreme Court nominations are inherently political. So it’s no surprise that they are drawn out for ideological or partisan reasons,” she wrote. “But district court nominations are different.”

Even before the current crisis, mounting caseloads and standoffs between the White House and Senate had lengthened the average time it took to get civil lawsuits to trial in federal courts by 63 percent and for criminal cases by 16 percent in the decade ending in 2013, according to a Syracuse University study of court data.

The practical impact of bottlenecks has raised warnings from judges appointed by both parties.

Jerome B. Simandle, chief judge of the federal district court in New Jersey and a 1992 George H.W. Bush appointee, told his state bar association that three emergency vacancies are leading to “untenable,” record caseloads for judges in the country’s ­second-busiest federal court.

“We really hope the U.S. Senate can move the nominations forward, not just for our court but for all courts. We can’t meet the demands of the public for fair and impartial courts without judges,” Simandle said in an interview.

He noted that during the 1992 election year when he was appointed, a Senate and White House held by opposing parties managed to have 53 district judges confirmed. The total so far this year is six.

Senate Republican leaders say they are confirming as many trial court judges as past Congresses.

A spokeswoman for Judiciary Committee Chairman Charles E. Grassley (R-Iowa) called continued attacks on his nominations record “unfounded and based on political rhetoric from paid political operatives and an increasingly desperate minority.”

As of last week, the panel had held hearings for exactly as many judicial nominations this Congress — 43 — as Sen. Patrick J. Leahy (D-Vt.) oversaw as chairman through May 2008, and had confirmed 325 Obama appointees, compared with 304 George W. Bush appointees, committee spokeswoman Beth Levine said in a statement.

“To say that President Obama hasn’t been treated fairly during his presidency isn’t based in reality,” Levine said. She called complaints a “made-up crisis,” given fluctuating annual vacancy rates.

But Leahy said once Obama took office, the Senate shifted from what Leahy in a statement called the Senate’s previous practice. “Deference to home state senators was no longer the norm and procedural delay after procedural delay quickly became the standard practice of the Republican caucus, whether they were in the minority or now in the majority,” creating a “vacancy crisis” in the lower courts, he said.

As those arguments play out, judges continue to retire or take senior status, and nomination hearings in the Senate have not kept pace with that wave.

Nearly 50 percent more judges — 239 — have stepped back from active status under Obama than did under George W. Bush at the same point in their presidencies, according to judicial records.

A Democratic-led Senate confirmed 58 district court judges during Bush’s last two years in office. Under Republican control, the Senate has confirmed 16 Obama nominees since 2014, judiciary data show.

The slowdown has blunted any shift to the left of lower courts in the usual ebb-and-flow of the two-party system.

As of last month, 52 percent of active federal district judgeships were held by appointees of Democratic presidents. Another 10 percent were vacant. By comparison, of judges now on senior status with reduced caseloads, 55 percent were named by Republicans.

The balance of the federal trial courts will be even more up for grabs for the winner of this year’s presidential election.

“In the long run, if all presidents get their fair share of nominees, then the courts will be balanced. And if there’s a period without confirmations at all, you lose that balance,” Scheindlin said in an interview.

Openings on the federal court that serves the District and those for Texas illustrate the stakes.

Washington’s influential U.S. district court oversees numerous high-profile lawsuits involving the federal government, such as an ongoing inquiry into Democratic presidential front-runner Hillary Clinton’s handling of emails as secretary of state and recent rulings striking down key parts of Obama’s Affordable Care Act health law and the District’s gun regulations.

As of late May, all but one of the 12 active judges were Democratic appointees, including nine named by Obama and confirmed since December 2010. Obama is set to have three more in the nominations queue, although their confirmation chances are unclear.

The lopsided political profile of the federal trial court in the District owes much to chance and generational turnover. No new judges joined the bench between November 2002 and December 2010, an eight-year gap that was the longest such spell since at least the 1970s. That period without new faces was caused mostly by the lack of openings before 2007, not delays in filling openings.

The impact of Obama’s appointments as openings occurred became clear when Richard W. Roberts, a 1998 Clinton appointee, unexpectedly stepped down March 16 as chief district judge, citing health reasons. On the same day, Roberts had been named in a lawsuit brought by a Utah woman who accused him of sexually assaulting her decades ago. Roberts’s attorneys have denied the allegation.

Roberts’s successor as chief judge — a role based on seniority and age — was Beryl A. Howell, 60, a former Democratic Senate Judiciary Committee counsel who was Obama’s first nominee. Howell joined the court a little more than five years ago and is the shortest-tenured chief judge to take the post at the court since the 1940s.

Howell cautioned against drawing conclusions about ­judges based on the party of the president who nominated them, while underscoring the importance of filling vacancies.

“When judges take the bench, they put on a black robe, and they leave their politics behind,” Howell said in a statement, “and a full bench of active judges is what every chief wants.”

If the Washington court’s Democratic tilt was largely a result of coincidence, open seats in Texas appear to be a result of political calculations, said Russell Wheeler, an expert on the federal judiciary at the Brookings Institution.

In the Lone Star State, where immigration and drug prosecutions have sent caseloads above 1,200 a year for some judges, 10 of 52 judgeships have gone unfilled for more than two years, on average.

Critics say delays in filling 20 percent of the bench in effect have kept Obama appointees from overturning the courts’ ­existing 25 to 17 GOP-appointee majority.

“While the imbalance in D.C. is pretty much a coincidence, the imbalance in the four Texas districts is mainly because the GOP senators have used their virtual veto power over nominations to prevent timely nominations,” Wheeler said.

Drew Brandewie, a spokesman for Sen. John Cornyn (R-Tex.), said that the White House, working with senators, named five nominees in March and that a bipartisan state committee of lawyers named by Cornyn and Sen. Ted Cruz (R-Tex.) is continuing to screen candidates. The Senate has confirmed 13 other Obama judicial nominees for Texas, he added.

Brandewie called the process of raising challenges to nominees a natural product of having a president of a different party than the state’s two senators and the party holding the Senate, a dynamic he said would be the same were party affiliations reversed.