Washington (CNN) -- Remember the Internal Revenue Service targeting of conservative groups?
It was the scandal du jour in Washington last month, now relegated to back-burner status after recent revelations of a vast government electronic surveillance apparatus created in the name of national security following the 9/11 terrorist attacks.
The announcement Thursday by the Obama administration that it would boost aid to Syria rebels because government forces there used chemical weapons further shifted attention away from the IRS controversy involving extra scrutiny given conservative groups seeking tax-exempt status.
Republicans continue trying to raise the issue, grilling FBI Director Robert Mueller about it at a congressional hearing on Thursday. They argue that the Obama administration used the tax agency to intimidate and harass political opponents.
Democrats respond that the independent inspector general who revealed the targeting blamed poor management, rather than political bias. Congressional sources on both sides say that interviews with IRS workers so far have found no political conspiracy.
What happens next depends on any further information from ongoing investigations. The IRS, the agency's inspector general at the Treasury Department, J. Russell George, the Department of Justice and GOP-led congressional committees are all looking into the matter.
Acting IRS Commissioner Danny Werfel, appointed by President Barack Obama to clean up the mess, said last week that he would release more information on the targeting once privacy issues had been worked out.
If the investigations fail to find a political effort to suppress activities by conservatives, the scandal will likely die a slow bureaucratic death of piecemeal reports in coming months.
However, if the multiple inquiries find evidence of guidance from Washington and even the White House, as claimed by Republicans, the scandal would instantly generate new headlines, more hearings and possible criminal proceedings.
Mueller told the House Judiciary Committee on Thursday's the FBI was investigating IRS targeting, and assured legislators that "to the extent there's any indication of criminal misconduct, we will follow the leads and the evidence wherever it takes us."
However, he declined to discuss the matter further because of the ongoing probe, prompting frustration from Republicans on the panel.
Conservative Rep. Jim Jordan, a fierce critic of the Obama administration, hammered Mueller with questions such as who was leading the investigation, how many investigators were assigned and whether they had interviewed groups victimized by the targeting.
When Mueller said he hadn't been briefed on those details, the Ohio Republican blew up.
"You can't even tell me who the lead investigator is?" he asked Mueller, who will step down soon after almost 12 years leading the FBI. "You can't tell me how many agents are assigned to the most important story in the country?"
Seven committee hearings so far on the matter revealed the partisan divide that permeates Washington.
Republicans called the targeting a conspiracy of Nixonian dimensions, while Democrats condemned it as bureaucratic rather than political malfeasance.
At the House Oversight Committee, GOP Chairman Darrell Issa of California and ranking Democrat Elijah Cummings of Maryland have engaged in a public dispute over interviews that panel investigators conducted with IRS workers involved in the targeting.
Earlier this month, Issa released excerpts of transcripts that he said showed IRS officials in Washington played a role in the targeting.
"This was a problem coordinated in all likelihood right out of Washington headquarters and we're getting to proving it," he told CNN on June 2.
"My gut tells me that too many people knew this wrongdoing was going on before the election, and at least by some sort of convenient, benign neglect, allowed it to go on through the election," Issa said. "I'm not making any allegations as to motive, that they set out to do it, but certainly people knew it was happening."
In response, the Oversight Committee's Democratic staff released further interview excerpts that Cummings said disproved any White House role. He challenged Issa to release the full transcript, which has yet to occur.
"Based upon everything I've seen, the case is solved," Cummings told CNN last Sunday. "And if it were me, I would wrap this case up and move on."
Meanwhile, the White House has tried to shift attention to other issues with events on student loan rates, health care reform and immigration legislation.
Top White House officials say they knew nothing of the targeting when it occurred. General Counsel Kathryn Ruemmler learned of a pending inspector general's report on April 24, 2013, according to White House spokesman Jay Carney.
When asked Wednesday if the full transcripts of interviews with IRS workers should be released, Carney said Issa had promised to do so.
He added that Cummings "has demonstrated that we have seen yet again some cherry-picking when it comes to the release of testimony, release of information," Carney added, referring to past instances when Republicans on the Oversight panel made public details on other issues that turned out to be incomplete or misleading.
The inspector general report last month found that an IRS unit in Cincinnati had used criteria that included conservative labels such as "tea party" to target groups seeking tax-exempt status for extra questioning. IRS rules prevent groups engaging in political activity from becoming tax exempt.
According to the report, the targeting began in 2010 and ended last year when senior IRS officials learned of it. It blamed a misguided effort to streamline handling of increased applications for tax-exempt status, exacerbated by unclear regulations regarding what constitutes political activity.
Republicans contend the targeting was political discrimination in the run-up to the 2012 election, and one of the GOP-led House committees heard from groups who detailed delayed handling of their requests, excessive questioning by the IRS for inappropriate information, and other problems.
Some conservatives also contend they faced IRS tax audits due to political targeting, but no evidence of such activity has turned up in investigations so far.
George told an earlier congressional hearing that his unit was investigating the possible use of other lists of criteria to trigger additional scrutiny of tax-exempt applications. He provided no details.
Meanwhile, the partisan bickering goes on.
The Republican National Committee released a video this week that accused the Obama administration of dodging responsibility. It included footage of IRS officials testifying before congressional committees, edited to highlight when they said they didn't know or were unable to remember details.
"Americans deserve answers to why their First Amendment rights were so egregiously violated," RNC Chairman Reince Priebus said. "Turning a blind eye and claiming not to know, or remember, what actions were carried out is no excuse for targeting individuals based on their beliefs. These are simple questions, and if they can't answer it raises another: what are they hiding?"
CNN's Kevin Liptak and Paul Steinhauser contributed to this report.