Military leaders edited intelligence reports about the Islamic State to downplay the threat posed by the terrorist organization, a congressional investigation has concluded.

Senior officials at U.S. Central Command "regularly provided line-in/line-out edits and wording changes" to intelligence reports that were provided to then-CENTCOM commander Army Gen. Lloyd Austin and "other senior customers." The edits rendered the final versions of those reports "consistently more optimistic" than analysis provided by career CENTCOM experts, according to a new report from the joint task force formed by members of three House committees and released on Thursday.

The lawmakers make clear that the intelligence problems arose while Austin led CENTCOM and Maj. Gen. Steven Grove led the CENTCOM Intelligence Directorate under Austin, although the report doesn't mention their names. Instead, the task force observed more politely that the problems did not exist when Austin's predecessor, Marine Gen. James Mattis, held the post. The CENTCOM reports improved once Army Gen. Joseph Votel replaced Austin as CENTCOM commander this spring and brought with him a new director of intelligence.

The rose-colored reports tinted the perception of the Islamic State by President Obama's personal intelligence advisers, the report suggests. That's because Grove, one of the officials accused by a whistleblower of manipulating the reports, regularly briefed some of the most senior intelligence officials in the U.S. government, including the Joint Staff director for intelligence and Director of National Intelligence James Clapper.

"These calls took place several times per week before daily intelligence briefings by the DNI to the president," the lawmakers found. "The frequency of these interactions could have provided CENTCOM leadership outsized influence on the material presented to the president outside of formal coordination channels."

No other military director participated in those special briefings, the report emphasizes. The degree to which these reports provided an incomplete picture of the Islamic State threat was exacerbated by the fact that CENTCOM Intelligence Directorate leaders failed to follow "analytic best practices" by barring their analysts from coordinating with analysts from other intelligence agencies. They also required all the reports to receive a final review from a newly-established Analytic Review Team.

Those "restrictions ... creat[ed] unnecessary stovepipes that centralized information within senior CENTCOM leadership channels," the report says. "Senior leadership involvement sometimes resulted in delays to the publication of intelligence products that could otherwise have provided critical warning to the CENTCOM commander, the IC [intelligence community], and national policy-makers."

The task force comprised three lawmakers: Reps. Ken Calvert, Mike Pompeo and Brad Wenstrup. Calvert is on the House Appropriations defense subcommittee, Pompeo is on the House Intelligence Committee and Wenstrup is on the House Armed Services Committee.

"After months of investigation, this much is very clear: from the middle of 2014 to the middle of 2015, the United States Central Command's most senior intelligence leaders manipulated the command's intelligence products to downplay the threat from ISIS in Iraq," Pompeo said. "The result: consumers of those intelligence products were provided a consistently 'rosy' view of U.S. operational success against ISIS. That may well have resulted in putting American troops at risk as policymakers relied on this intelligence when formulating policy and allocating resources for the fight."

Wenstrup, a lieutenant colonel in the Army Reserve, said he understood intel isn't always certain, but argued that's not a justification for "excluding" alarming information from reports. "Possibilities and probabilities can be just as critical for decision makers," he said. Additionally, despite nearly nine months of review, we still do not fully understand the reasons and motivations behind this practice and how often the excluded analyses were proven ultimately to be correct."

CENTCOM leadership interviewed by the task force denied willfully requiring the intel reports to provide only "optimistic" views of the Islamic State, but the investigators couldn't find any instances of the reports being edited in a way that made the terrorists seem more dangerous than the original drafts would have suggested. They defended making the edits, however, by arguing that they had access to "operational reporting" provided by U.S. military entities in Iraq that was more credible than the analysis provided by their own experts.

"The Joint Task Force can find no justifiable reason why operational reporting was repeatedly used as a rationale to change the analytic product, particularly when the changes only appeared to be made in a more optimistic direction," the report says. "By supplanting analytic tradecraft with unpublished and ad hoc operational reporting, Joint Intelligence Center (JIC) leadership circumvented important processes that are intended to protect the integrity of intelligence analysis."

Senior analysts across CENTCOM disliked this micromanaging, as evidenced by an annual survey conducted in 2015 in which 40 percent of the analysts who participated complained "that they had experienced an attempt to distort or suppress intelligence in the last year." The comments accompanying the survey, which were provided in a redacted form to the task force, emphasized that the reports were being subjected to a one-way ratchet.

"Of the 71 comments, 32 included direct allegations of distortion of intelligence to fit a positive narrative, and an additional 26 comments raised broader tradecraft or process concerns," the report says.

CENTCOM officials also misled Congress, according to the comments. "Of note, four separate comments alleged that products were delayed or altered to avoid conflicting with senior officials' testimony to Congress," the task force added.

In faulting CENTCOM leadership, the task force partially-corroborates the White House's assessment of the matter. Senior Obama administration officials blamed Austin for Obama's most infamous Islamic State gaffe, telling The Atlantic that the president referred to Islamic State as a "J.V. team" based on the general's assurance that the terrorist group would be "a flash in the pan."

Grove has been transferred from CENTCOM. He is now the director of the Army Quadrennial Defense Review Office at the Pentagon. Austin retired from military service in April.

"Over the last three years as Commander, U.S. Central Command, General Austin has overseen military operations in one of the most demanding regions of the world, including operations in Iraq and Afghanistan and our broader counter-ISIL campaign," Obama said at the time. "I have relied on his wise judgment and steadfast leadership to help me navigate the many challenges we find there."