The DoD "Staff" that it creates have no operational control or function. It creates a lot of overhead and multiple chains of command - all of which are generally bad for military organizations.
Here's the only cogent observation on this topic which i have seen so far. There is no basis for claiming the position is unconstitutional, although it is worth noting these provisions of the Constitution:
Article One, Section 8, final paragraph reads:
To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.
Although i feel fairly certain that if Congress were to attempt to circumscribe or in any way define the powers and duties of such an officer, the Shrub would squeal, and start another witless and wasteful power struggle between the executive and legislative branches.
Article II, Section 2, second paragraph reads:
He shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur; and he shall nominate, and by and with the Advice and Consent of the Senate, shall appoint Ambassadors, other public Ministers and Consuls, Judges of the supreme Court, and all other Officers of the United States, whose Appointments are not herein otherwise provided for, and which shall be established by Law: but the Congress may by Law vest the Appointment of such inferior Officers, as they think proper, in the President alone, in the Courts of Law, or in the Heads of Departments.
So, either the Shrub will need to secure the appointment of this officer from the Senate, or he will have to secure a bill from the Congress (both houses) to authorize him to appoint this officer. However, it would be questionable whether or not such an officer would constitute "[an] inferior officer" in the terms of the Constitution. The Senate likely would, and probably should, consider such an appoint as equivalent to a Head of Department, and require the executive to secure the consent of the Senate, after having advised with that body.
This looks like a "fall guy" position. However, i don't accept the argument that this is just a case of the Shrub appointing someone because he cannot carry out his duties as commander in chief. All Presidents who have gone to war (with a few notable exceptions) have relied upon their military advisers, and with good reason--this is their area of expertise, and not necessarily that of the President. Madison appointed some stunningly incompetent Secretaries of War--but this was obvious to the Congress and to the nation at large in the War of 1812, and they were replaced. William Eustis was blamed for initial incompetence and defeats in the war, and had to step down. His replacement, John Armstrong, wasn't much better, because his expectations of the military and the militia were unrealistic. He was forced to resign because of the burning of Washington, which, however, was one disaster for which he couldn't reasonably be blamed. He was replaced by James Monroe, but Monroe did not take office until after the treaty had been negotiated--it was a war nobody wanted, on either side of the Atlantic, although the Americans would have been more enthusiastic if Jefferson had had the moral courage to go to war in 1807 or 1808.
One of the early and true "heroes" of that war was Winfield Scott. When Mr. Polk managed to get the war he wanted with Mexico, Scott was the senior officer in the United States (he was a Major General with the earliest date of rank, which made him senior to all other officers). He and Mr. Polk cordially disliked one another, but Scott always acted with a very competent professionalism, and never challenged his subordination to the civilian authority. Polk and his political advisers mistrusted Scott, and considered that Scott would use the war as a basis to run against Polk in the next election, so they did all they could to hamstring him, and ran a campaign to make him look incompetent and ridiculous in the public press, which Scott unwittingly aided with his rather pompous style of speech and his insistence on military protocol and his love of gaudy uniforms and militarily correct behavior. His men called him "Old Fuss and Feathers" as a result, and his "hasty plate of soup" remark in a letter to the President was a disaster, as Polk's boys published the letter, and used it to make him ridiculous.
Thomas Hart Benton wanted to run the war, and lobbied his political allies in the Senate to appoint him Major General, and give him control of the war. They were not enthusiastic. Apparently, someone pointed out to him that even as a Major General, he would be subordinate to Scott, so he began lobbying the Congress to make him a Lieutenant General. That effectively sank his military barge, however; George Washington was the only American who had by then held the rank of Lieutenant General (after he left the Presidency), and no one in Congress was dull-witted enough to think that Benton had any qualifications for such an exalted position. Finally, the Polk administration decided that they would have to use Scott, and he was sent to Mexico after Zachary Taylor had defeated the Mexicans in the "northern department," and when it became apparent that it was not militarily feasible for Taylor's army to march on the Mexican capital from his position south of the Rio Grande. Most of Taylor's command was transferred to Scott, and Scott used the Navy to outflank Santa Anna's position, landing at Vera Cruz. (Such effective cooperation between the Army and the Navy became a permanent American military policy thereafter.) Scott's march on the city of Mexico, defeating the Mexicans at every turn, and despite being heavily outnumbered, gained him the sincere praise of military men in Europe--but Polk's campaign against him in the press effectively assured that he was never going to be a serious presidential candidate. Ironically, Polk's boys worked so hard to discredit Scott, and during an unpopular war, that they apparently failed to notice the popularity of Zachary Taylor, who succeeded Polk in the White House in 1848.
During the American Civil War, Lincoln constantly said that he needed to find a man who "understands the numbers." His appointments to Secretary of War were first questionable, and then wise. First, he appointed Simon Cameron, for political reasons. Cameron and his cronies immediately began stealing everything which wasn't nailed down. Lincoln's friend from his days in the House, and by then a Senator from Maine, Fessenden, once implied to Lincoln that Cameron was stealing--and this during a public reception at the White House. Lincoln asked him: "Surely you're not saying that Secretary Cameron would steal?"--to which Fessenden replied: "Well, he wouldn't steal a red-hot stove." Confronted publicly by Cameron, Fessenden then said: "I'm sorry I said that you wouldn't
steal a red-hot stove." Cameron didn't last long, and Lincoln replaced him with Stanton, formerly the Attorney General, who served in strictly an administrative capacity, and with great competence.
Lincoln appointed Henry Halleck to clean up the mess which John Frémont had left in Missouri, and an impressive mess it was. Halleck was an irritating personality who managed to piss off just about every officer who ever served under him, and he was also highly competent, cleaning up the mess in the Western Theater. Because he quarreled with Grant and Don Carlos Buell, he managed to ruin the career of the latter, although he promoted the former (against his own inclinations), and supported Grant's plans to work closely with the Navy to penetrate and take control of Tennessee (once again, against his own inclinations--he considered Grant an unreliable alcoholic, but gave in to Lincoln's demand that Grant be given responsibility, because he [Grant] was aggressive). Halleck only took command in the field personally after Shiloh, leading the advance to Corinth, Mississippi, and treating Grant like a dog in the process. Eventually, Halleck returned to Washington, after McClellan managed to squander his wonderful opportunities before Richmond in 1862. Grant was given command of the West, although Buell's command was set up separately from his (Buell ranked with Halleck, having been made a Major General slightly later than Halleck. By contrast, Grant was then a Major General of United States Volunteers, but only held the rank of Colonel in the regular army).
Lincoln would come to describe Halleck as "only a first rate clerk," but that was needed, as well. Another contemporary said that Halleck was anxious to ". . . [make] sure that no blame of any sort fell on him." So, Halleck would advise his subordinate officer to conduct operations which he would not have risked himself. The result was happy for the United States, though, because that meant that he gave Grant a long lead, and Grant took every advantage of it. In his memoirs, Grant describes his march on Leadville, Missouri, when he was still just a regimental commander with rank as a U.S. Volunteer. He described how he was eaten up with worry for four days, but advanced on the Confederates none the less. When he arrived, he found the Confederate camp abandoned, the southern commander having taken counsel of his fears and retreated. Grant says that this taught him a valuable lesson--the other man is just as scared as you are. He never looked back.
Grant gave up attempting to enter Mississippi from the north, and began his campaign to take Vicksburg; with many fits and starts, and overcoming enormous obstacles, he succeeded on July 4, 1863. Lincoln had found his man who understood the numbers. Grant was brought east, became only the second man in American history to be promoted Lieutenant General (in the regular army, which meant he outranked everyone), and took charge of the military operations of all the armies. He kept Halleck, who was, after all, a first rate clerk, and who kept things so well organized that contemporary observers described Secretary of War Stanton as chronically bored.
Since that time, American Presidents have left the actual control of military operations in the hands of competent military officers, with one notable exception. In the second world war, this meant that Admiral King and General Marshall respectively ran the Navy and the Army, with excellent results. In 1964, however, all such matters were left in the hands of Robert MacNamara, who had been Secretary of Defense in Kennedy's administration, and continued to hold the position in Johnson's administration. I cannot say (and wouldn't) that the war would have been handled any differently, nor any better, if MacNamara had left military matters in the hands of the professional officers, but MacNamara's "micro-managing" of the Vietnam War has been widely criticized, and probably with great justice.
What the Shrub may actually intend with this position neither i, nor anyone else here, can say. The basic principle, however, of having a military man in charge of military operations, while still subject to civilian control, is not only nothing unreasonable, it makes good sense. Those who are willing to criticize every decision the Shrub makes ought to be glad that there is an opportunity for a military professional to do this job. I do, suspect, though, that Fishin' is right that this will only add unnecessary layers of command and control to a situation already badly mismanaged.