How Does the Difficulty Adjustment Mechanism Affect the Cost of a 51% Attack?

The difficulty adjustment mechanism (DAM) is designed to keep the average block time consistent despite changes in total network hashrate. If an attacker suddenly introduces a large amount of hashrate for a 51% attack, the DAM will eventually increase the difficulty, making the attack more expensive to sustain over time.

However, the DAM is usually slow, meaning the initial cost is the primary barrier, but the ongoing cost is continuously inflated.