WASHINGTON (CNN) -- A Republican campaign to vilify President Barack Obama's administration over Internal Revenue Service targeting of conservative groups strengthened Wednesday, with GOP congressional leaders alleging criminal activity and demanding answers.
All 45 Senate Republicans sent the White House a letter that called for the administration to "comply with all requests related to congressional inquiries without any delay" involving the controversy.
It called the scandal "yet another completely inexcusable attempt to chill the speech of political opponents and those who would question their government, consistent with a broader pattern of intimidation by arms of your administration to silence political dissent."
House Speaker John Boehner went further, telling reporters that "clearly someone violated the law" in what an IRS inspector general's report described as delayed processing of applications by groups associated with the political right wing.
Senate Republican leader Mitch McConnell also suggested criminal behavior occurred, saying that the "very serious" allegations involve "an effort to bring the power of the federal government to bear on those the administration disagreed with in the middle of a heated national election."
"It actually could be, could be criminal and we are determined to get the answers," McConnell said.
Boehner was more definitive, declaring that "my question is who's going to jail over this scandal?"
Meanwhile, GOP Sen. John Thune of South Dakota called Wednesday for the acting commissioner of the IRS to step down.
The clearly coordinated attacks were part of a GOP effort to increase pressure on the Obama administration over the controversy, one of three potential scandals that has the White House on the defensive less than four months into the president's second term.
According to the report by the agency's inspector general released Tuesday, the IRS developed and followed a faulty policy to determine whether the applicants were engaged in political activities, which would disqualify the groups from receiving tax-exempt status.
The controversial move began in early 2010 and continued for more than 18 months, the report said, declaring that "the IRS used inappropriate criteria that identified for review Tea Party and other organizations applying for tax-exempt status based upon their names or policy positions instead of indications of potential political campaign intervention."
In a statement released late Tuesday, Obama called the report findings "intolerable and inexcusable."
"The federal government must conduct itself in a way that's worthy of the public's trust, and that's especially true for the IRS. The IRS must apply the law in a fair and impartial way, and its employees must act with utmost integrity. This report shows that some of its employees failed that test," the president said.
Obama also said he has directed Treasury Secretary Jack Lew "to hold those responsible for these failures accountable."
Also Tuesday, Attorney General Eric Holder said the Justice Department had launched a criminal investigation into whether the IRS politically targeted some conservative groups.
"The FBI is coordinating with the Justice Department to see if any laws were broken in connection with those matters related to the IRS," Holder said at a briefing.
However, law professor Jonathan Turley of George Washington University said it was unlikely that anyone would end up facing criminal charges.
"It's a violation of federal law, but rarely to people go to jail for it," Turley told CNN on Wednesday.
More often, criminal charges come from federal officials lying to cover up wrongdoing, rather than from following orders, he said.
"The most likely conclusion is no one would be charged, if you look at history," Turley added.
IRS officials, according to the report, did not consult anyone beyond the agency about the development of the additional screening criteria. They believed that the criteria they came up with was a screening shortcut meant to help with the influx of applications, the report said.
McConnell and other Republicans have questioned whether others in the administration outside the IRS, such as the Treasury Department and the White House, had any role.
The controversial actions began after the 2010 Supreme Court ruling in the Citizens United case that greatly expanded the ability of corporations, unions and other organizations to participate in election spending, though not through direct contributions to candidates or parties.
After the ruling, the number of politically oriented groups seeking tax exempt status as social welfare organizations under section 501 (c) (4) of the federal tax code increased greatly at a time when the federal government including the IRS was dealing with austerity measures that reduced or stagnated personnel and resources.
The IRS top watchdog found that the criteria used to flag potential political applications resulted in substantial
delays and the request of unnecessary information from the groups.
Among the criteria used by IRS officials to flag applications was a "Be On the Look Out" list, which was discontinued in 2012, according to the report.
The criteria included:
-- Whether "Tea Party," "Patriots" or "9/12 Project" was referenced in the case file.
-- Whether the issues outlined in the application included government spending, government debt or taxes.
-- Whether there was advocating or lobbying to "make America a better place to live."
-- Whether a statement in the case file criticized how the country is being run.
-- Whether it advocated education about the Constitution and the Bill of Rights.
The investigation by the Treasury inspector general for tax administration was initiated after congressional complaints began to surface in the media in 2012 that the IRS was targeting conservative groups and holding up applications.
"Whether the inappropriate criterion was shorthand for all potential political cases or not, developing and using criteria that focuses on organization names and policy positions instead of the activities permitted under the Treasury regulations does not promote public confidence that tax-exempt laws are being adhered to impartially," the report said.
The IRS welcomed the report, saying that it agreed that aspects of its original approach in handling the influx of tax-exempt applications was inappropriate.
"The IRS is required by law to determine if organizations are engaging in a legally permissible level of political activity. Centralizing these cases was necessary to achieve consistent treatment," it said in a statement.
In a written response included in the report, the IRS commissioner of the Tax Exempt and Government Entities Division said there was no criminal behavior behind the actions of the agents, but rather inefficient management.
"We believe the front-line career employees that made the decisions acted out of a desire for efficiency and not out of any political and partisan viewpoint," the commissioner wrote.
The report found that all of the applications that were sent to the Determinations Unit "experienced substantial delays in processing."
"Although the processing of some applications with potential significant political campaign intervention was started soon after receipt, no work was completed on the majority of these applications for 13 months," it said.
The report's findings indicate that of the 298 cases reviewed by the IRS inspector general as potential political cases not eligible for tax exempt status: 72 contained the name "tea party," 11 contained "9/12" and 13 contained the word "patriots," according to the report. There were 202 cases that did not contain any such reference.
Of those applications still open for review, 160 cases were open from 206 days to more than three years -- through two election cycles.
Among the recommendations made by the Treasury inspector general: The IRS must better document reasons why applications are chosen for review, develop a process to track requests for assistance, develop and provide training to employees before each election cycle and immediately resolve outstanding cases.
The report also called on Treasury to develop guidelines to explain social welfare activity -- the primary factor in obtaining tax-exempt status.
"Although the IRS has taken some action, it will need to do more so that the public has reasonable assurance that applications are processed without unreasonable delay in a fair and impartial manner in the future," the report said.
Lois Lerner, director of tax-exempt organizations for the IRS, said the activity highlighted in the report took place at the IRS office in Cincinnati, which handles applications for 501(c)(4) status.
But documents suggest at least three other IRS offices did the same.
Letters provided to CNN show IRS officials in Washington and California contacted conservative groups to demand more information before approving the groups' requests for tax-exempt status.
The American Center for Law and Justice, a legal group representing numerous conservative organizations, provided CNN with four such letters: one each from IRS offices in Washington; Cincinnati; El Monte, California, and Laguna Niguel, California.
The IRS did not respond to CNN's request for comment regarding the letters.
White House spokesman Jay Carney told reporters Tuesday that he's "confident" no one at the White House was involved in the practice.
Asked about complaints by some Republican lawmakers for the past couple of years that conservative groups were being unfairly targeted, Carney said he is "sure some people knew about the stories. But we were not aware of any activity or any review by the inspector general."
The Republican-led House Ways and Means Committee, which oversees the IRS, will hold a hearing on Friday. Steve Miller, the acting IRS commissioner, and the Treasury inspector general investigating the complaints,
J. Russell George, are scheduled to testify.
CNN's Kevin Liptak, Josh Levs, Kevin Bohn, Jake Tapper and Chelsea J. Carter contributed to this report.
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