This is a somewhat tricky question to answer because the legal definition of treason often includes criterion that the more popular sense of the word treason often lacks. For example, Pound would claim in 8 May 1945 declaration during his interrogation that:

Hitler and Mussolini were simple men from the country. I think Hitler was a saint, and wanted nothing for himself. I think that he was fooled into antisemitism and it ruined him. That was a mistake. When you see the mess that Italy gets into by bumping off Mussolini, you will see why someone could believe in some of his efforts.

Such pro-fascist attitudes like Pound's are naturally rather disconcerting, but they are not really actionable sentiments for a legal charge of treason. Pound himself often took umbrage that he was a traitor to his country. When the FBI indicted Pound in absentia in 1943, he countered by with a statement that he was merely engaging in free speech:

I understand that I am under indictment for treason...I do not believe that the simple fact of speaking over the radio, wherever placed can in itself constitute treason. I think that must depend on what is said, and on the motives for speaking. I obtained the concession to speak over Rome with the following proviso. Namely that nothing should be asked of me contrary to my conscience or contrary to my duties as an American citizen. I obtained a declaration on their part of a belief in "the free expression by those qualified to have an opinion."... I have not spoken with regards to this war, but in protest against a system which creates one war after another, in series and in system. I have not spoken to the troops, and have not suggested that the troops mutiny or revolt.

After Pound's capture, his somewhat harsh imprisonment and contributed to an apparent mental breakdown. There was some debate over whether or not this breakdown was real or feigned. Edd Johnson of the Philadelphia Record interviewed Pound, in which the poet likened Hitler to Joan of Arc and seemed more interested in talking about Chinese ideograms than his impending trial. Johnson noted that Pound was hale, and that "if he is off his rocker, it does not show in any of the usual signs of nuttiness." Yet, Pound as a prisoner seemed more intent on refining what would later become known as the Pisan Cantos than framing his own defense and sharing his insights into literature, art, and philosophy with his guards. One of his guards would later become a college security guard and would claim to know far more about art than the student body because of some fellow he spent guarding in 1945. This erratic (although typically Pound-esque) behavior meant trying him on his indictment of treason was problematic. His attorney argued in in November 1945 that Pound was unfit to plea on the grounds of insanity and he was remanded to St. Elizabeth's Hospital for observation. A majority of psychiatrists who interviewed Pound found him unfit mentally and unable to stand trial. The result of this judgement was that Pound would be institutionalized for the better part of twelve years. Although the indictment still stood over Pound's head like a sword of Damocles, his status as an elite literary figure (he won the prestigious Bollingen Prize for the Pisan Cantos while being treated) coupled with the emerging Cold War meant there was less urgency in the Justice Department for charging Pound was officially dismissed in 1958.

The charge of treason against Pound was compounded not only by his mental state, but also the content of his radio broadcasts. In contrast to other Axis radio personalities like Lord Haw-haw or Tokyo Rose, Pound's broadcasts were a mixture of his philosophical ramblings about the intersection of art and his interpretation of geopolitics. The literary scholar Forrest Read called Pound's Rome broadcasts "a confused mixture of fascist apologetics, economic theory, anti-Semitism, literary judgment, and memory." His broadcasts tended to never speak about the war directly, but allude to a political situations in their abstract forms. Although Pound evinced a particularly nasty streak of antisemitism in his broadcasts, he tended to not argue for specific actions for Allied troops to surrender and turn against the Jews. In short, Pound's broadcasts were highly intellectual and very rambling that it was difficult to pin a specific treason charge upon.

Sources

Feldman, Matthew. Ezra Pound's Fascist Propaganda, 1935-45. [Basingstoke]: Palgrave Macmillan, 2013.

Moody, A.D. Ezra Pound: Poet: A Portrait of the Man and His Work, Volume III: The Tragic Years. Oxford: Oxford University Press, 2015.