The republicans will claim that he has something to hide.
The dems can say he’s the first person they’ll call when they take the House. 
Just wait until after the lame duck, I’m sure he’d gladly testify once Schiff has the gavel and the Dems conduct a proper investigation. Until then, I don’t blame him for brushing off the Republicans.
This is what an actual political witch hunt looks like.
The two committees have been investigating partisan bias at the Justice Department for several months
After January, Dems will show you how to do a real investigation of partisan bias.
The “Justice” Republicans are really in love with that dossier. It was an unfinished, incomplete piece of work according to its author. But Hannity & Jim Jordan etc. are obsessed with it. Like attack dogs all pulling on the same bone, on and on they go. I’m glad this guy is pleading the 5th.
All the committees have to do is grant this toad immunity, then he has to testify or face obstruction charges.
Meanwhile
Vast archive of tweets reveals work of trolls backed by Russia and Iran
Two misinformation campaigns spent years sowing discord in US and elsewhere
Vast archive of tweets reveals work of trolls backed by Russia and Iran | Internet | The Guardian
He has already testified to two committees - I have read his testimony and it was lengthy and detailed. He is not going to be charged with obstruction because he doesn’t want to get involved with this GOP Trump-driven witch hunt against Mueller.
It’s his right to refuse.