An easy way to think about these hypotheticals is to look at real life examples and postulate how things could have been different.
Using Bush as an example, we already know his administration condoned torture, set up black sites around the world, weakened US prestige and influence by using force on every occasion, and illegally attacked critics. By using conservative media, who wanted to be used, they were able to sway public opinion for years to force their agenda, force opposing parties to kowtow to them in fear, all while making the country less safe through corruption and incompetence.
Imagine had Bush been just a little worse. Imagine instead of leaking Valerie Plame’s name, he ordered her husband, the one who criticized the whole Nigeria yellowcake story, arrested for spilling secrets to the enemy. He could have rendered the both of them to a black site, never to be seen again. Congress was in his lap for most of 2001-2005, until the Iraq war started turning badly. Had he actively imposed more media blackouts other than the whole pictures of US coffins, spread more misinformation about how the war was going, how the death rates were, the GOP might have been able to hold on to most of their seats in 2006.
Let’s say gerrymandering happened a few years earlier, and they didn’t lose so many seats. Let’s say the Tea Party never formed and simply those crazy right wing extremists were in Congress just one session earlier. Housing bubble pop, recession happened, yet millionaires and billionaires still got richer and still had their taxes lowered. Just this year, Mitt Romney floated Paul Ryan’s plan, which gave even more tax cuts to the rich and had tax rates for the poor and middle class go up. Let’s say all that happened just a few years earlier.
In one 8 year term, an Evil President can take a hundred billion dollar surplus and turned it into a trillion dollar deficit. Justified American torture, attacked 2 countries, enshrined the right of the rich to exploit the poor, destroyed American prestige and influence, bankrupted the country, threw us into a recession, protected banks over homeowners, pardoned criminals, arrest dissenters, destroy the social safety net, and made laws to ensure they’d be hard pressed to lose another election. That’s probably what an Evil President can do, and more