If a miner attempts to manipulate the blockchain by altering transactions or adding fraudulent data, the decentralized nature of the blockchain helps to prevent such manipulation. Other nodes in the network validate and verify transactions independently, so any attempt at manipulation would be detected and rejected by the majority of the network. Additionally, the consensus mechanism, such as Proof of Work or Proof of Stake, ensures that miners must invest resources or stake tokens to participate, making it economically impractical to manipulate the blockchain.