The mempool is whatever you want it to be. You set the fee by which a transaction rides past your node. And yes, multiple attacks have been attempted by the m

The mempool is whatever you want it to be. You set the fee by which a transaction rides past your node. And yes, multiple attacks have been attempted by the miner side on full nodes. The most recent being Segwit2X, which didn't get off the ground because convincing 100k nodes that their version of Bitcoin was different wasn't going to work.