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While Attorney General Eric Holder is taking heat for his department's seizure of reporter records, the U.S. attorney who is personally overseeing those investigations is himself starting to face complaints that he's gone too far in pursuing leaks.

Ronald Machen Jr., the U.S. attorney for the District of Columbia, was nominated by President Obama in 2009 and now runs the biggest federal prosecutor office in the country. His hundreds of attorneys handle everything from gang violence to corruption.

But in recent years, leak investigations have become a hallmark of his portfolio. And his dogged pursuit of the squeaky wheels in government has led him into the tenuous -- and some say unprecedented -- territory of lumping in leakers with journalists.

"What's astonishing here is that never before has the government argued that newsgathering -- in this case, asking a source to provide sensitive information -- is itself illegal," Gabe Rottman, legislative counsel at the American Civil Liberties Union, told FoxNews.com.

Machen was an early and frequent campaign donor to Obama during the 2008 election, giving close to the maximum amount allowed by law. He gave $2,300 in the general election and nearly as much during the primary.

Yet Machen was arguably chided this week, though not by name, when Obama announced a review into the Justice Department's guidelines for investigations that involve journalists. He said he was "troubled" by the developments and that journalists should not be "at legal risk" for doing their jobs.

Machen's investigation into accused leaker Stephen Jin-Woo Kim raised exactly that concern. As part of that case, federal officials obtained a search warrant for Fox News reporter James Rosen's personal emails, and seized phone records for various Fox News lines. Officials were able to obtain the warrant on the pretext that Rosen was likely a criminal "co-conspirator" along with Kim. Though Rosen was not charged, media and other watchdog groups have described that step as "chilling."

Aside from his involvement in the Kim case, Machen was one of two federal prosecutors tapped by Holder in June of last year to lead the investigation into a string of high-profile security leaks.

It was presumably that investigation that led his office to seize two months of phone records from the Associated Press. Machen first notified the news service of the seizure earlier this month.

Some worry that not only has Machen gone too far but he may be too close to the White House to remain objective. Machen was an Obama campaign contributor and supporter before being appointed by the president in 2009.

"As a former volunteer for Obama for America, contributor to the president's election campaign, and having assisted with the vetting of vice presidential candidates, Machen is a far cry from the beacon of independence and impartiality that something as sensitive as this investigation demands," Sen. John Cornyn, R-Texas, told FoxNews.com.

Lawmakers have joined members of the media in asking probing questions about the cases. Fourteen Republicans on the House Judiciary Committee recently sent a letter to Deputy Attorney General James Cole asking for details on the department's decision to seize the AP's telephone records. Cole supervised the probe in Holder's absence and signed off on the subpoenas.

For Machen and Obama, their connection dates back to Harvard Law School. Machen, a 1994 graduate, has been quoted in several publications calling Obama, a 1991 graduate, a "legend."

Machen was one of the first people who donated to the president's U.S. Senate campaign 2003.

Years later, when the highly coveted U.S. attorney job opened up, Obama turned to his friend and political supporter. On Dec. 24, 2009, Obama nominated Machen to head up the largest and arguably most powerful prosecution office in the country. The Senate confirmed Machen's nomination two months later.

Machen now runs an office that has 300 attorneys who prosecute both federal and local crimes. In D.C. alone, there were an estimated 20,000 cases handled by his staff last year. These include everything from misdemeanor drug possession charges to high-profile allegations of fraud and terrorism. And it's exactly that kind of broad-based power that makes some people nervous.

The Obama administration has brought more prosecutions against so-called leakers under a law known as the Espionage Act than any administration in U.S. history.

Rottman says the pattern of promoting friends and political supporters is nothing new and was practiced during the Bush and Clinton years as well. The problem, Rottman says, is when the government's efforts to go after leakers start to strangle press freedoms.

"National security leaks are criminal and put American lives on the line, and federal prosecutors should, of course, vigorously investigate," Florida Republican Sen. Marco Rubio said in a statement. "But we expect that they do so within the bounds of the law, and that the investigations focus on the leakers within the government -- not on media organizations that have First Amendment protections and serve vital functions in our democracy."

Calls to Machen's office and the White House for comment were not returned.

But Machen's office issued a statement earlier this week defending against some of the criticism that had surfaced in the media. The office clarified that at no point did officials "wiretap the phones of any reporter or news organization" or obtain records from the "computer servers of any news organization."

"We take seriously our obligations to follow all applicable laws, federal regulations, and Department of Justice policies when grand jury subpoenas are issued for phone records of media organizations, and strive to strike the proper balance between the public's interest in the free flow of information and the public's interest in the protection of national security and the effective enforcement of our criminal laws," the office said.