Cause and effect. Action, reaction. Trump just couldn't keep his mouth shut - he just couldn't keep his stubby little thumbs away from Twitter - and he made things markedly worse for himself by threatening Mueller. Same thing happened with Comey.
These myriad committee hearings - whether they be here, in the U.S., at the level of an obscure Commons committee or an extraordinary Senate Intelligence Committee prying back the lid on Donald Trump's corrupt administration - are good for democracy. They may look democracy look bad, in the short term. Sure. But, in the long term, they improve it, too.