'But once this goes to court and is immediately thrown out as baseless, the harm (undermining confidence in the president) will already have been done.'
Maybe or maybe not. Jmo, but I'm guessing part of Trump's uptick in popularity is due to more and more people waking up to the political motivation of Mueller's witch hunt. Iow, hounding and harassing a sitting president could well be a losing strategy. If so, count on the Democrats to double down on it.