Why I think a MacArthur nomination is very unlikely:
"MacArthur’s main rivals in 1944 were New York governor Thomas Dewey, former presidential candidate and Republican Party president Wendell Willkie, and Minnesota governor Harold Stassen. Vandenberg believed MacArthur’s only chance for the nomination was a deadlocked convention, which he knew could be engineered. Then at the appropriate time MacArthur’s name would be submitted and the nomination secured.
"But for that to work, MacArthur’s name had to be kept off state primary ballots because any defeat would burst the “infallible” bubble, wrecking everything. Vandenberg and his group’s efforts to control the MacArthur-for-President movement unraveled in Illinois and Wisconsin, where MacArthur’s name managed to get on the primary ballots. Confident of his popularity, MacArthur refused to sign a document from them requesting that his name be withdrawn. MacArthur’s home state, on his father’s side, was Wisconsin. As such MacArthur had to win Wisconsin. Instead he lost – big time, coming in third behind Dewey and Stassen. The resounding victory in Illinois was a hollow one, because his opponent was an unknown.
"Then a batch of letters put paid to the movement.
"Freshman Republican Congressman Arthur Miller from Nebraska was a MacArthur supporter. Miller’s first letter to the general, dated Sept. 18, 1943, stated in part: “I am certain that unless this New Deal can be stopped this time our American way of life is forever doomed. You owe it to civilization and the children yet unborn to accept the nomination.”
"Of all his flaws, perhaps MacArthur’s greatest was a tender ego, which made him a sucker for flattery. In December 1943, Army chief of staff General George Marshall visited MacArthur in Port Moresby. During one of their discussions, MacArthur began a sentence with “My staff,” only to have Marshall interrupt, “You don’t have a staff, general. You have a court.”
"MacArthur’s response to Miller included the sentence, “I unreservedly agree with the complete wisdom and statesmanship of your comments.” A correspondence had begun.
"On April 14, 1944, Miller, without consulting the general, released MacArthur’s letters to the press thinking they would reinvigorate the general’s campaign. Instead, their highly partisan contents destroyed what was left of it. Vandenberg called Miller’s action “a tragic mistake.” MacArthur was mortified. He tried to fight back, stating truthfully that the letters “were never intended for publication,” but it was too late.
"Upon the advice of Sen. Vandenberg, on April 30, 1944, MacArthur issued a statement that closed with the passage: “I request that no action be taken that would link my name in any way with the nomination. I do not covet it nor would I accept it.”..."
https://www.defensemedianetwork.com/stories/macarthur-for-president/
So can we plausibly see MacArthur being nominated? Only if (1) he doesn't allow his name to be entered in any primary, even in his "home state" WI which he thought he could win, (2) he resists the temptation to reply to flattering letters from anti-New Deal Republicans and thus seem to endorse their politics, and (3) the convention develops into a deadlock among Dewey and Willkie and Stassen and maybe some favorite sons, with the convention eventually turning to MacArthur.
I have serious doubts about (3)--as long as Dewey is the only major "stop Willkie" candidate who can actually
actively campaign he is likely to have the nomination locked up before the convention. But in any event, (1) and (2) seem very unlikely to me--they would require MacArthur to keep his ego in check. Good luck with that!
