National flags represent the country... or the state?
Ok, in the books it is the country, but the state is who actually manages the country. And of course, patriotism and nationalism are powerful tools, so it makes sense to use them.
If you are lucky, the state (and those who support the status quo) will not use those tools in a partisan way, but for the common good (defending the country from the enemy, calling for ethical behavior of the population, etc.)
If you are not lucky, then... Well, calling someone a traitor is a very strong emotional argument, avoids all the work of having to address the points that the critics are trying to argue and limits the risk of the critics succeeding. And being in a position of authority gives you a lots of bonus points.
I mean, how could someone who loves SO MUCH the flag do bad things to the country the flags represent?
Well, if you believe that what your side is doing is the right thingTM, then using the tools at your disposal to weaken the opposition is the ethical thing to do (it is for their own sake, even if they cannot realize it).
And if you just want to have your side win and do not care about anything else, you are lucky! You can do exactly the same and claim that you are doing it out of patriotism.
The more flag waving, the more right you are.
Which leads to:
A competition to link your image and your ideas to the flag (and by extension the country), with exclusion of any other possibility. There is no display of affection too extravagant.
Once you have established that the country (and by extension the flag) is linked to your ideas, some of those who do not share your ideas may become alienated as the flag is no longer the country's but yours. Bad for the country but good for you (and ultimately that means good for the country, isn't it?) There are even blockbusters about that behavior
And of course, a rational discourse of the situation is to be avoided. The appeal to emotion must be constant.
And to finally address the question, this is far from old. Remember:
McCarthy committee was not of "Soviet" or even "Communist" Activities, it was of "Un-American Activities" (which allowed it to attack people as dangerous as for the security of the USA as Humphrey Bogart, Orson Welles or Charlie Chaplin).
The First Red Scare (1919) saw strikers being called "lenin agents" (and treated accordingly).
If you want to go further, the title of the The South Vindicated from the Treason and Fanaticism of the North Abolitionist (1836) -H. Manly leaves no doubt that those who oppose slavery are nothing but traitors (and certainly traitors are not worthy of the flag).
etc., etc., etc.