This situation reminds me of George Romney's "brainwashing" snafu, George Romney presidential campaign, 1968 - Wiki (emphasis added):

The "brainwashing" reference had been an offhand, unplanned remark that came at the end of a long, behind-schedule day of campaigning. By September 7 it had found its way into prominence at The New York Times. Eight other governors who had been on the same 1965 trip as Romney said no such activity had taken place, with one of them, Philip H. Hoff of Vermont, saying Romney's remarks were "outrageous, kind of stinking ... Either he's a most naïve man or he lacks judgment." The connotations of brainwashing, following the experiences of American prisoners of war (highlighted by the 1962 film The Manchurian Candidate), made Romney's comments devastating, especially as it reinforced the negative image of Romney's abilities that had already developed. The topic of brainwashing quickly became newspaper editorial and television talk show fodder, with Romney bearing the brunt of the topical humor. Senator Eugene McCarthy, running against Johnson for the Democratic nomination, said that in Romney's case, "a light rinse would have been sufficient." Republican Congressman Robert T. Stafford of Vermont sounded a common concern: "If you're running for the presidency, you are supposed to have too much on the ball to be brainwashed." After the remark was aired, Romney's poll ratings quickly nosedived, going from 11 percent behind Nixon to 26 percent behind.
So, one of the factual issues today is whether a thorough brain scrubbing or a light rinse was given out.

Jack Goldsmith writes at Lawfare, Psy-ops Against Congress - Count Me as Skeptical (emphasis added):

First, Congress exercises a lot of control through appropriations over military operations, especially COIN operations that require throwing around a lot of U.S. dollars. It is commonplace for soldiers in the field to try to present an attractive picture on the ground for visiting congressional delegations in order to persuade them to continue or increase funding for missions. It is also commonplace to frame the pitch to address the interests, pet projects and peeves, inclinations, concerns, and the like, of visiting officials. Doing so requires research.

Second, as far as I can tell, the factual charges against General Caldwell come from a single source, Colonel Michael Holmes, the leader of one of Caldwell’s information operations units. Hastings states that Caldwell and his subordinates asked Holmes to “conduct an IO campaign against” visiting officials. But the facts offered in support of this supposed operation are thin. Holmes was (by his account) ordered to research and provide background assessments on the visitors, and prep the General for his meetings. When Holmes complained about the order, it was clarified to specify that he should “only use publicly available records to create profiles of U.S. visitors.” Holmes colors this seemingly innocent tasking in dark shades. He says that Caldwell sought a “deeper analysis of pressure points we could use to leverage the delegation for more funds” and claims that Caldwell asked: “How do we get these guys to give us more people? What do I have to plant inside their heads?” The “plant inside their heads” phrase conjures up an image of Caldwell asking Hastings to help him play psychological tricks on the visiting congressmen. But at bottom the story says only that Holmes was asked to do backgrounders on visiting dignitaries and to advise General Caldwell about how to brief the dignitaries in a persuasive way.

Third, as the Washington Post notes, Hastings’ article “did not cite evidence of false or misleading information being provided to the senators and other visitors.” Nor does Hastings provide much support for his claim that Caldwell acted illegally. Holmes apparently believed that what he was asked to do violated the Smith-Mundt Act of 1948. I believe this law, as amended, prevents the State Department, not DOD, from directing foreign propaganda at domestic audiences. (Hastings says as much.) But I also believe that there are laws, presidential directives, and military regulations that prohibit DOD from using true psychological operations against members of Congress. (Hastings mentions, but does not cite or quote, prohibitions in Defense Authorizations.) Whatever the law might say, Hastings’ only support for the assertion that Caldwell acted illegally comes from Holmes himself, who is apparently not a lawyer. Hastings also cites an email from a JAG to Holmes, which stated: “Using IO to influence our own folks is a bad idea . . . and contrary to IO policy.” The JAG did not state that what Holmes claimed Caldwell asked him to do was illegal.

Fourth, Hastings throws out so many unsupported and unfair zingers against Caldwell that it makes me question the credibility of the entire story. There are too many to list, but one of the most egregious (already noted by Andrew Exum) is when Hastings says that Caldwell “seemed more eager to advance his own career than to defeat the Taliban.” The evidence for this charge is Holmes’ claim that Caldwell “seemed far more focused on the Americans and the funding stream than he was on the Afghans.” But this unsupported assertion, even if true, does not mean that Caldwell cared more about his career than about the Afghanistan mission. The reality is that keeping Congress informed and on board is a vital element both of American democracy and success in Afghanistan.

Fifth, Hastings notes that Holmes was subsequently subject to an AR 15-6 investigation for “going off base in civilian clothes without permission, improperly using his position to start a private business, consuming alcohol, using Facebook too much, and having an ‘inappropriate’ relationship with one of his subordinates.” Hastings makes the investigation seem like retaliation. But on the evidence presented, it is also possible that Holmes’ feeding of the story to Hastings was retaliation for the 15-6 investigation. The Hastings story does not provide enough information to permit us to decide.
Jack's five general points need to be resolved - or the contested factual positions laid out - before anyone can analyze whether what went on was "legal" or "illegal" (which does not necessarily equate to "terminal dumbness"). Like Jack, I'm not an SME in this legal area.

Regards

Mike