The senators could have voted to convict convict during the impeachment trial.

That would have been more than a speed bump. They had the opportunity to act, chose not to (well except for Romney).

You can very fairly blame them for not removing him. I don't think you can blame them for the storming as Trump has the support of the base. They do not.

Trump's been riling his base up with lies and almost everyone important in the republican party has been doing nearly nothing to disagree. They're supposed to be about half of our elected leadership. They can be blamed for inaction.

If they were openly and clearly disagreeing with Trump, then they wouldn't be at fault. But they're giving tacit approval.

I would blame those who haven't taken issue with the spreading of conspiracy theories and certainly those who spread conspiracy theories when it is convenient for them that leads to this kind of thing.

Cruz, Hawley, et al. helped escalate the situation to this point. This would not have happened if they weren't planning on protesting certification in the first place. There are degrees of culpability here. It obviously starts with the mob itself, then Trump, then his supporters in congress, then other Republicans who hesitated to accept the election results, etc.

Most of them came out against Trump only so long as it didn't matter, and in the least effectual way they could. They also almost universally stopped even pretending once he was elected.