Jonathan Ernst/ REUTERS Committee Chairman U.S. Representative Darrell Issa (R-CA) holds a House Oversight and Government Reform Committee hearing on Capitol Hill in Washington, May 22, 2013.

The IRS scandal was an early Christmas gift to Republicans. Flagrant abuse of power by a villain voters already hate is the kind of bombshell that could wreak havoc for months, casting a shadow of scandal on the White House and unifying an opposition party wrestling with internal divisions. Democrats conceded the IRS’s decision to target conservative groups was “outrageous,” as President Barack Obama put it. Just a week ago, the controversy seemed set to sidetrack the president’s legislative agenda. Republicans prepared for a summer of embarrassing hearings.

But an overzealous prosecutor can bungle even an open-and-shut case, and that’s what Democrats hope to portray Darrell Issa, the chairman of the House Oversight and Government Reform committee and the President’s self-styled nemesis. For years, Issa has launched a series of probes into alleged White House malfeasance, from the “Fast and Furious” gun-running controversy to loans the Department of Energy made to the failed green-energy company Solyndra. In both instances, Issa went after high-level scalps — only to see the investigations peter out without claiming top officials, such as Attorney General Eric Holder, who was under scrutiny in “Fast and Furious.” Now Democrats are pointing to his habit of claiming conspiracy, as well as a series of intemperate remarks Issa has made about the IRS case, in an attempt to deflect attention from the scandal by discrediting the inquisitor.

(VIDEO: Holder Lashes Out at Rep. Issa, Calling Conduct ‘Shameful‘)

“As late as last week the administration’s still trying to say there’s a few rogue agents in Cincinnati, when in fact the indication is they were directly being ordered from Washington,” Issa said Sunday in an interview on CNN’s State of the Union. During that interview, Issa, 59, also criticized White House Press Secretary Jay Carney for blaming the scandal on a “local rogue,” and called Carney a “paid liar.”

Issa’s accusations were accompanied by excerpts the committee released from interviews conducted with two unidentified workers at the IRS office in Cincinnati. In one excerpt, a worker scoffs at the notion that employees in the bureaucratic backwater could be solely responsible for the politically motivated targeting. “It’s impossible,” the employee says. “As an agent we are controlled by many, many people. We have to submit many, many reports. So the chance of two agents being rogue and doing things like that could never happen.”

“One of the things we’ve heard,” says a spokesperson in Issa’s office of the committee’s interviews with IRS employees in Cincinnati, “is how frustrated and thrown under the bus they feel.”

It’s hard to assess the accuracy of Issa’s claims. The Oversight committee hasn’t released the full transcripts of those interviews, or identified the employees. Nor has Issa explained why he believes the conspiracy to target conservative political outfits applying for 501(c)(4) status stretches deep into the agency’s Washington headquarters. The Treasury Inspector General found that IRS offices in DC did contribute to inappropriate delays when some conservative groups applied for tax-exempt status. But it found no political influence from the White House, or anyone else, in those actions.

“Strong words from Mr Grand Theft Auto and suspected arsonist/insurance swindler,” tweeted former White House senior adviser David Plouffe. The remark was a reference to Issa’s checkered past. The seven-term Congressman became one of the wealthiest members of the legislative branch when he entered in 2001, thanks to a company he founded that manufactured popular car alarms. But as a young adult, Issa ran into some trouble with the law, according to a profile by the New Yorker‘s Ryan Lizza. He was indicted for stealing a car (the case was dismissed), accused by a business associate of burning down a factory to collect the insurance money (he was never charged) and pleaded guilty to possessing an unregistered firearm after a traffic stop. (Issa was given probation for the offense.)

(MORE: The Real IRS Scandal)

Carney, for his part, declined to get into a ‘back and forth” with Issa. But Steny Hoyer, the House Democratic whip, told reporters Tuesday that the congressman’s ad hominem attack and unsubstantiated allegations that the scandal was orchestrated from Washington “indicates a real political bias on his part.” Hoyer added: “It’s hard to trust somebody who makes assertions without evidence.”

Senate Republicans also think Issa is getting ahead of himself. “I don’t believe this was something thought up in the Cincinnati office, but I have no evidence that goes to the White House,” Republican Senator Lindsey Graham said Sunday on Fox News. “You can go too far,” he added. “Jay Carney is not the issue here.” Graham’s partner in crime, Arizona Senator John McCain, said Republicans should “let the facts come out” rather than lob insults.

Publicly, House Republican leaders have stood with Issa’s inquisition. “Chairman Issa is providing tough, effective and appropriate oversight in the face of White House obstruction,” says Michael Steel, a spokesman for Speaker John Boehner. House Majority Leader Eric Cantor ducked questions Tuesday about Issa’s handling of the matter. But Issa’s offices says the message from colleagues has been clear: “Keep doing what you’re doing,” says an aide to Issa, who says Republican leaders “share the chairman’s view in terms of his concern about the issues. They want him to be thorough.”

Issa’s office says the committee is in the early stages of a long term investigation. On Sunday, Issa said the committee still had 18 more interviews to conduct with IRS officials. “We’re not making predictions about where this is going to lead us,” says an aide. But despite his bluster, Issa has so far produced no evidence tying anyone outside the independent agency to the scandal.

Privately, some Republicans fret that Issa’s overzealousness could blur the lines between the committee’s legitimate oversight role and partisan witch-hunting. And even Democrats wonder why Issa won’t let the investigation run its course. “This isn’t good for us, but it’s not as bad as he’s making it out to be either,” says one longtime Democratic operative. But like Issa, Democrats probably don’t know yet where the probe will lead. And their scramble to target Issa suggests they’re searching for their own scapegoat in case it’s nowhere good.

MORE: New IRS Scandal Echoes a Long History of Political Harassment

Correction appended, June 5:

The original text of this story said that the “alleged perpetrators” of the Fast and Furious and Solyndra matters were “cleared by independent investigators.” A Department of Justice Inspector General’s report into Fast and Furious found fault with and held accountable several state and federal officials, though not Holder or other top Obama Administration targets.