One of the biggest challenges facing the president in draining the Washington Swamp is ferreting out the activists who continue to pursue a progressive agenda in federal agencies.

Richard C. Pilger has headed the Election Crimes Branch in the Public Integrity Section of the Criminal Division of the U.S. Justice Department since 2010. Appointed by former Attorney General Eric Holder, Mr. Pilger is in charge of prosecuting public corruption cases, and specifically “voter fraud and campaign financing offenses.”

Despite evidence pouring in that some local and state election officials are allowing massive numbers of noncitizens, felons and other ineligible names to remain unchallenged on voter registration rolls across the nation, Mr. Pilger’s department has responded with a Parisian-style shrug.

Annual reports to Congress during Mr. Pilger’s tenure from 2010 to 2015 (the latest published report), list only three cases of prosecuted vote buying schemes — one in Texas in 2014 and two in Kentucky in 2012 — but not a single case involving fraudulent voter registrations.

It’s not as if the unit hasn’t had opportunities handed to them on a silver platter.

“Over the past eight years, the Public Integrity Section and particularly its Election Crimes unit has ignored potential cases of voter fraud by failing to investigate or prosecute them,” said Hans von Spakovsky, a former member of the Federal Election Commission and a senior legal fellow at the Heritage Foundation

“That includes information on hundreds of noncitizens in Virginia who illegally registered and voted in violation of federal law. Apparently, Rip Van Winkle is the role model of the lawyers who work there when it comes to protecting the integrity of our elections.”

Mr. von Spakovsky is a member of the Presidential Advisory Commission on Election Integrity and a Policy Board member of the American Civil Rights Union, which has been suing counties in several states to force them to clean up their voter rolls.

A few years ago, the Fairfax County, Virginia Election Board, on which Mr. von Spakovsky served, sent a letter informing Mr. Pilger that 278 noncitizens were found on the county’s voter rolls, which indicated a strong possibility that vote fraud was occurring.

“The Justice Department never did a thing about it,” Mr. von Spakovsky recalled. “We also sent it to the Commonwealth’s Attorney of Fairfax and the U.S. Attorney for the Eastern District of Virginia. Again, nothing happened.”

Opponents claim that vote fraud is either non-existent or trivial. But if officials ignore clear evidence of corrupt voter rolls, vote fraud can go undetected for years — or forever.

A recent, contested town council election with a razor-thin margin in Phenix City, Alabama is a case in point. More than 85 people have been found on the voter rolls who illegally listed a business address instead of a residence. Since the election was decided by only 10 votes, it has gone to a runoff on Dec. 19. Registrars didn’t bother checking whether voters’ addresses are actually residences. This is so ripe for abuse that the local chapter of the NAACP has called for an investigation into vote fraud.

In Virginia, two studies by the Public Interest Legal Foundation (PILF), “Alien Invasion” and “Alien Invasion II,” document the enormity of the problem that DOJ officials like Mr. Pilger are ignoring. Here’s a summary from “Alien Invasion II”:

“Virginia election officials quietly removed 5,556 voters for non-citizenship between 2011 and May 2017; 1,852 of those removed as noncitizens cast ballots; a total of 7,474 illegal ballots were cast from the pool of removed noncitizens.”

The response over at the DOJ’s Election Crimes Branch? Yawn.

While apparently uninterested in vote fraud, Mr. Pilger was quite interested in aiding the Internal Revenue Service’s extra scrutiny of tea parties and other conservative nonprofits.

“In 2010 he reached out to then IRS tax-exempt chief Lois Lerner about prosecuting nonprofits that engaged in political activity for making false statements on their tax returns,” according to The Wall Street Journal. “In an October 2010 email exchange, Ms. Lerner and Mr. Pilger discussed the transfer of data on 501(c) organizations. The Justice Department ended up with a database of 1.1 million documents, including protected taxpayer information.”

In April 2014, members of the House Oversight and Government Reform Committee sent a letter to the DOJ asking for materials concerning emails that surfaced between “Pilger and the Internal Revenue Service’s Lois G. Lerner where they discussed singling out and prosecuting tax-exempt applicants, at the urging of a Democratic senator.” After DOJ balked, committee Chairman Darrell Issa issued a subpoena for the documents.

On May 6, 2014, Mr. Pilger refused to answer 34 questions from the committee’s staff. Shades of Ms. Lerner taking the Fifth when questioned about targeting the tea parties.

Why doesn’t anything ever happen to these people? I mean, legally. Ms. Lerner, who has retired with full benefits, has asked that records be sealed because she says she fears for her safety.

At least Ms. Lerner can’t do any more damage from her former perch at the IRS.

But that leaves Mr. Pilger. What on earth is he still doing in charge of the Election Crimes Branch at the Department of Justice?

Inquiring Swamp drainers need to find out.

• Robert Knight is a senior fellow for the American Civil Rights Union.