Hello everyone,

Recently, I've been reading a lot about how the bitcoin governance/development process works.
I read the book "The blocksize War", and one thing that caught my attention was how central in the blocksize debate was the role of miners vs nodes.

So I've been trying to understand what's the role of miners vs nodes in securing the network, and I have a couple of questions/doubts that I'd love to get answered.

As far as I understand, miners are in charge of confirming transactions, they secure the network by making it costly to falsify transactions (create unforgeable costliness, as Nick Szabo would put it). On the other hand, nodes are in charge of validating, propagating, and keeping a copy of transactions, they make sure that miners act according to the protocol rules, not acting maliciously (i.e. introducing false transactions, or try to double spend).

My question is, in order to make a successful 51% attack: One would need to have 51% of mining power, 51% of nodes, or both?
For example, in the case that someone gets to have 51% of mining power, could nodes protect the network from that attack by not validating transactions? In other words, could the network be secure if the nodes are decentralized even if the mining pool is not?

IMO, in the answer to this question lies the key of what keeps the network decentralized.

I'm new to this forum. So I'm sorry if this question would better fit into another topic. In that case, just make me know and I will move it to the right place.