Nice chapter, nice work that Huey Long is doing. I hope the Populist Party can survive and thrive if Long lives or dies. If he dies and the culprit is an ideological enemy of the Populists, the party will see a major boost in power and prestige. When it comes to the race issue, I hope the Populists become strong supporters of Civil Rights, maybe the Populists can run ads about how both the Republicans and Democrats want to keep blacks down? Good that Brazil is coming to the Americans side with Germany going fully anti-christian. South America will hopefully be a much more stabler and prosperous place TTL with a strong country like Brazil to be at it's head. Keep up the good work.
The thing about the Populists is that they are, above all, Longists, they go along with Huey and his proposals of a strong Executive, accessible welfare, combat on big business and... that's really it. There are southerners in the Progressive party who do not want to support Civil Rights, Long didn't even get a "Little Rock" incident yet to show how committed he actually would be towards Desegregation. Sure, there are many progressives but the focus has always been on wealth rather than race and there is not a short supply of those who would be very generous towards the Blacks when it comes to welfare and still oppose integration.
If Huey dies there isn't a very clear successor in such a young party. It could be Russel Long, it could be LBJ, but it would be a power vacuum right before an election when they stand at their best chance of getting national sympathy (aka the LBJ 1964 effect). This is a Party which never held a true convention for the Presidency yet, the first it was just Long making the Party and being unanimously supported as candidate. That's not even counting what happens if all the corruption ends up discovered, that is a sure way to make the Populists be stillborn.
And it would be hard to run ads that the Republicans want to run down the Blacks when they are the main supporters of Civil Rights as the Democrats were reduced to essentially Dixiecrats. What I could see is fear mongering on the economical aspect, the classic "they will take out your welfare and give the money to the rich".
As for Brazil, between 52 and 56 they were considered a "hostile" nation, but not a hostile nation. The Integralists are nationalists and fundamentalist Catholics who despise the US, but they hate even more the Nazis (don't even need to mention the Chinese), Salgado also personally has taken a dislike for Mussolini due to his Atheism and have better links to Portugal. Ironically, it is Ideological and religious radicalism which prevented half of South America from going straight into the Linz Pakt.