I mean teachers unions popular with the general public.
And I can think of one potential POD which was mentioned earlier, the Boston police strike of 1919.* Now, if the police announce the strike ahead of time or strike for an extended period, that's irresponsible and there's no way around that. There really isn't. But if the police have a 2-hour lightning strike where they keep a skeleton crew and don't announce, that's smart. There could even be a running joke that if only the criminals had known ahead of time! And following, let's suppose the union is successful in getting the public to see the grievances.
And let's further suppose the mayor of Boston orders both sides back to the negotiating table to bargain in good faith. Now, that's probably not exactly within the purview of the mayor. But let's say both sides accept this, largely as a way to save face.
The police and the city negotiate an alright deal. And then, (?) perhaps over the years most citizens come to see a public employees union as mainly about collective bargaining, with strikes only a rare bird (?). Well, maybe.
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* Earlier I said the Boston police strike was during FDR's time in office. That's a mistake. The Boston police strike happened in 1919 during the "Red Scare" period in Wilson's last couple of years. And perhaps during Wilson's incapacitation when Mrs. Edith Wilson and Naval doctor and president's personal physician Dr. Cary Grayson were essentially running the executive branch.