Three things happened in the ex-FBI boss Comey's testimony:
1. There was no new ground broken which would have been called as new evidence of 'obstruction of justice' by Trump. All that big yawn you hear from Republican Congress members, it is because 'it could have been worse...' kind of relief Republicans are having.
2. But Comey laid his case effectively. Trump practically threatened Comey to end Flynn investigations, made it clear what he expected from Comey, then he fired him and finally went public saying Russia investigation was on his mind. It is difficult to see other than what is obvious here - Trump wanted Comey to end investigations and Comey paid the price for not obliging Trump. In a sense, there does not have to be a new evidence since Comey - with seven pages of written testimony and oral one today; established very conclusively that there was a clear attempt by Trump to stop Comey. This in itself is very powerful.
3. As Comey said, special counselor Mueller will have to determine whether Trump action constitutes an 'obstruction of justice' or not. But what Comey achieved is he made the 'liar' label stick to Trump. In the Court of American Public, more are likely to believe Comey's case that Trump tried to defame him and the Bureau untruthfully. Politically this is a big deal too. American Public knows not to take Trump literally and all politicians lie. (At least that is the 'meme' with Trump supporters!). But in this case, American People also know stakes are high.
Indeed far from unshackling himself, Trump will continue to be under a cloud with further loss of his credibility. Democrats are going to cherish this slow dripping.